SUMMARY

This summary highlights some of the information in this proxy statement/prospectus. It may not contain all of the information that is important to you. To understand the merger fully and for a more complete description of the terms of the merger, you should read carefully this document, the documents incorporated by reference, and the Annexes to this document, including the full text of the merger agreement included as Annex A. Please also read “Where You Can Find More Information.”

The Merger Parties’ Businesses (page 90)

Enterprise Products Partners L.P.

Enterprise is a publicly traded Delaware limited partnership, the common units of which are listed on the NYSE under the ticker symbol “EPD.” Enterprise was formed in April 1998 to own and operate certain natural gas liquids (“NGLs”) related businesses of EPCO. Enterprise is a leading North American provider of midstream energy services to producers and consumers of natural gas, NGLs, crude oil, petrochemicals and refined products. Enterprise’s midstream energy asset network links producers of natural gas, NGLs and crude oil from some of the largest supply basins in the United States, Canada and the Gulf of Mexico with domestic consumers and international markets. Enterprise’s assets include approximately: 52,000 miles of onshore and offshore pipelines; 220 million barrels (“MMBbls”) of storage capacity for NGLs, petrochemicals, refined products and crude oil; 14 billion cubic feet (“Bcf”) of natural gas storage capacity; 24 natural gas processing plants; 22 NGL and propylene fractionators; six offshore hub platforms located in the Gulf of Mexico; a butane isomerization complex; NGL import and LPG export terminals; and octane enhancement and high-purity isobutylene production facilities.

Enterprise’s midstream energy operations include: natural gas gathering, treating, processing, transportation and storage; NGL transportation, fractionation, storage, and import and export terminaling; crude oil and refined products transportation, storage and terminaling; offshore production platforms; petrochemical transportation and services; and a marine transportation business that operates primarily on the United States inland and Intracoastal Waterway systems and in the Gulf of Mexico.

Enterprise is owned 100% by its limited partners from an economic perspective. Enterprise is managed and controlled by Enterprise GP, which has a non-economic general partner interest in Enterprise. Enterprise GP is a wholly owned subsidiary of Dan Duncan LLC (“DDLLC”), a private affiliate of EPCO. Enterprise conducts substantially all of its business through its operating company, Enterprise Products Operating LLC (“EPO”).

Enterprise’s principal executive offices are located at 1100 Louisiana Street, 10th Floor, Houston, Texas 77002, and its telephone number is (713) 381-6500.

Oiltanking Partners, L.P.

Oiltanking is a publicly traded Delaware limited partnership, the common units of which are listed on the NYSE under the ticker symbol “OILT.” Oiltanking engages in the terminaling, storage and transportation of crude oil, refined petroleum products and liquefied petroleum gas. Through its wholly owned subsidiaries, Oiltanking Houston, L.P., a Texas limited partnership (“OTH”) and Oiltanking Beaumont Partners, L.P., a Delaware limited partnership (“OTB”), Oiltanking owns and operates storage and terminaling assets located along the United States Gulf Coast on the Houston Ship Channel and in Beaumont, Texas.

Oiltanking’s principal executive offices are located at 1100 Louisiana Street, 10th Floor, Houston, Texas 77002, and its telephone number is (713) 381-6500.

Relationship of Enterprise and Oiltanking (page 93)

Enterprise and Oiltanking are currently under common control. At October 1, 2014, Oiltanking was owned 98.0% by its limited partners and 2.0% by its general partner, Oiltanking GP. On October 1, 2014, Enterprise acquired, directly or through its wholly owned subsidiaries, Oiltanking’s general partner and approximately 66% of the limited partner interests in Oiltanking, or 54,799,604 units (including 38,899,802 Oiltanking common units issued upon the conversion of subordinated units on November 17, 2014). Oiltanking GP and the 66% of Oiltanking’s common units are currently owned by an indirect wholly owned subsidiary of Enterprise.

Enterprise is controlled by DDLLC and EPCO. EPCO and DDLLC are each controlled by three voting trustees, pursuant to the EPCO Inc. Voting Trust Agreement dated April 26, 2006 (the “EPCO Voting Trust Agreement”) and the Dan Duncan LLC Voting Trust Agreement dated April 26, 2006 (the “DDLLC Voting Trust Agreement”), respectively. The current EPCO voting trustees are Randa Duncan Williams, Ralph S. Cunningham and Richard H. Bachmann. The current DDLLC voting trustees are also Ms. Williams, Dr. Cunningham and Mr. Bachmann.

Neither Oiltanking nor Enterprise has any employees. All of the operating functions and general and administrative support services of Oiltanking and Enterprise are provided by employees of EPCO pursuant to an administrative services agreement (“ASA”) or by other service providers.

Some of the executive officers of Enterprise GP are directors of Oiltanking GP, including Bryan F. Bulawa, William Ordemann and Michael C. Smith, and some employees of Enterprise GP are directors or executive officers of Oiltanking GP, including Laurie H. Argo and Robert D. Sanders. For information about the common executive officers and employees of Enterprise GP and Oiltanking GP, and these executive officers’ relationships with EPCO and its affiliates and the resulting interests of Oiltanking GP directors and officers in the merger, please read “Certain Relationships; Interests of Certain Persons in the Merger.”

Structure of the Merger and Related Transactions (page 66)

Pursuant to the merger agreement, at the effective time of the merger, a wholly owned subsidiary of Enterprise will merge with and into Oiltanking, with Oiltanking surviving the merger as an indirect wholly owned subsidiary of Enterprise, and each outstanding common unit of Oiltanking held by Oiltanking public unitholders will be cancelled and converted into the right to receive 1.30 Enterprise common units. This merger consideration represents a 5.6% premium to the closing price of Oiltanking common units based on the closing prices of Oiltanking common units and Enterprise common units on September 30, 2014, the last trading day before Enterprise announced its initial proposal to acquire all of the Oiltanking common units owned by the public. Relative to the respective closing prices for Enterprise and Oiltanking common units on November 10, 2014, the day before the parties entered into the merger agreement, the 1.30 exchange ratio represents a 10.4% premium to Oiltanking unitholders.

In connection with the merger, EPO will not receive any consideration for the continuation of its limited partner interests in Oiltanking, Oiltanking GP will not receive any consideration for the continuation of its general partner interests or incentive distribution rights in Oiltanking, and Enterprise will be admitted as a limited partner of Oiltanking and be issued a number of Oiltanking common units equal to the number of Oiltanking common units held by Oiltanking public unitholders prior to the effective time.

If the exchange ratio would result in an Oiltanking public unitholder being entitled to receive a fraction of an Enterprise common unit, then such Oiltanking public unitholder will receive cash from Enterprise in lieu of such fractional interest in an amount equal to such fractional interest multiplied by the average of the closing price of Enterprise common units for the ten consecutive NYSE full trading days ending at the close of trading on the last NYSE full trading day immediately preceding the day the merger closes.

Once the merger is completed and Oiltanking common units held by Oiltanking public unitholders are exchanged for Enterprise common units (and cash in lieu of fractional units, if applicable), when distributions are declared by the general partner of Enterprise and paid by Enterprise, former Oiltanking public unitholders will receive distributions on their Enterprise common units in accordance with Enterprise’s partnership agreement. For a description of the distribution provisions of Enterprise’s partnership agreement, please read “Comparison of the Rights of Enterprise and Oiltanking Unitholders.”

As of December 31, 2014, there were 1,937,324,817 Enterprise common units and 83,128,494 Oiltanking common units outstanding. Based on the 28,328,890 Oiltanking common units outstanding at such date that are owned by Oiltanking public unitholders and eligible for exchange into Enterprise common units pursuant to the merger agreement, Enterprise expects to issue approximately 36,827,557 Enterprise common units in connection with the merger.

Based on the $40.30 closing price of Enterprise common units on November 10, 2014 (the last full trading day before Enterprise and Oiltanking entered into and announced the merger agreement), the exchange ratio of 1.30 Enterprise common units for each outstanding Oiltanking common unit, and the 28,328,890 Oiltanking common units owned by Oiltanking public unitholders, the value of the merger consideration to be received by such holders was approximately $1.4 billion, or $52.39 for each Oiltanking common unit.

Support Agreement (page 65)

In connection with the merger agreement, Oiltanking, Enterprise and EPO entered into the support agreement dated as of November 11, 2014. Pursuant to the support agreement, Enterprise and EPO have agreed to vote any Oiltanking common units owned by them or their subsidiaries in favor of adoption of the merger agreement and the merger at any meeting of Oiltanking unitholders. In addition, pursuant to the support agreement, EPO granted an irrevocable proxy to a member of the Oiltanking Conflicts Committee to vote such units accordingly. EPO currently owns directly 54,799,604 Oiltanking common units representing approximately 66% of the outstanding Oiltanking common units. The support agreement will terminate upon the completion of the merger, the termination of the merger agreement, the Oiltanking Conflicts Committee making a change in recommendation or the written agreement of EPO, Enterprise and Oiltanking.

Directors and Officers of Enterprise GP and Oiltanking GP (page 99)

DDLLC, the sole member of Enterprise GP, has the power to appoint and remove all of the directors of Enterprise GP. Enterprise GP has indirect power to cause the appointment or removal of the directors of Oiltanking GP, an indirect wholly owned subsidiary of Enterprise. DDLLC is controlled by the DDLLC voting trustees under the DDLLC Voting Trust Agreement. Each of the executive officers of Enterprise GP is currently expected to remain an executive officer of Enterprise GP following the merger. The DDLLC voting trustees have not yet determined whether any directors of Oiltanking GP will serve as directors of Enterprise GP following the merger. In connection with Enterprise’s acquisition of Oiltanking GP on October 1, 2014, F. Christian Flach, a former Oiltanking GP director, was appointed as a director of Enterprise GP. In the absence of any changes, we expect the current directors of Enterprise GP to continue as directors following the merger.

The following individuals are currently executive officers of Enterprise GP, and those persons signified with an asterisk (*) also currently serve as directors of Oiltanking GP.

Market Prices of Enterprise Common Units and Oiltanking Common Units Prior to Announcing the Proposed Merger (page 29)

Enterprise’s common units are traded on the NYSE under the ticker symbol “EPD.” Oiltanking’s common units are traded on the NYSE under the ticker symbol “OILT.” The following table shows the closing prices of Enterprise common units and Oiltanking common units on September 30, 2014 (the last full trading day before Enterprise announced its initial proposal to acquire all of the Oiltanking common units owned by the public) and on November 10, 2014 (the last full trading day before Enterprise and Oiltanking entered into and announced the merger agreement).

The Special Unitholder Meeting (page 40)

Where and when: The Oiltanking special unitholder meeting will take place at 1100 Louisiana Street, 10th Floor, Houston, Texas 77002 on February 13, 2015 at 8:00 a.m., local time.

What you are being asked to vote on: At the Oiltanking meeting, Oiltanking unitholders will vote on the approval of the merger agreement and the merger. Oiltanking unitholders also may be asked to consider other matters as may properly come before the meeting. At this time, Oiltanking knows of no other matters that will be presented for the consideration of its unitholders at the meeting.

Who may vote: You may vote at the Oiltanking meeting if you owned Oiltanking common units at the close of business on the record date, January 2, 2015. On that date, there were 83,128,494 Oiltanking common units outstanding. You may cast one vote for each outstanding Oiltanking common unit that you owned on the record date.

What vote is needed: Under the merger agreement and Oiltanking’s partnership agreement, holders of a majority of the outstanding Oiltanking common units must affirmatively vote in favor of the proposal in order for it to be approved. Enterprise and EPO have agreed to vote any Oiltanking common units owned by them or their subsidiaries in favor of adoption of the merger agreement and the merger at any meeting of Oiltanking unitholders. EPO currently directly owns 54,799,604 Oiltanking common units (representing approximately 66% of the outstanding Oiltanking common units), which is sufficient to approve the merger agreement and the merger under the merger agreement and Oiltanking’s partnership agreement.

Recommendation to Oiltanking Unitholders (page 51)

The members of the Oiltanking Conflicts Committee considered the benefits of the merger and the related transactions as well as the associated risks and determined unanimously that the merger agreement and the merger are advisable, fair and reasonable to, and in the best interests of, Oiltanking and the Oiltanking unaffiliated unitholders. The Oiltanking Conflicts Committee also recommended that the merger agreement and the merger be approved by the Oiltanking Board and the Oiltanking unitholders. The Oiltanking Board has also approved the merger agreement and the merger and recommends that the Oiltanking unitholders vote to approve the merger agreement and the merger.

Oiltanking unitholders are urged to review carefully the background and reasons for the merger described under “The Merger” and the risks associated with the merger described under “Risk Factors.”

Oiltanking’s Reasons for the Merger (page 51)

The Oiltanking Conflicts Committee considered many factors in making its determination and recommendation that the merger agreement and the merger are fair and reasonable to and in the best interests of Oiltanking and the Oiltanking unitholders. The Oiltanking Conflicts Committee viewed the following factors, among others described in greater detail under “The Merger — Recommendation of the Oiltanking Conflicts Committee and the Oiltanking Board and Reasons for the Merger,” as being generally positive or favorable in coming to its determination and its related recommendations:

The Oiltanking Conflicts Committee considered the following factors to be generally negative or unfavorable in making its determination and recommendations:

Overall, the Oiltanking Conflicts Committee believed that the advantages of the merger outweighed the negative factors.

Opinion of the Oiltanking Conflicts Committee’s Financial Advisor (page 55)

In connection with the merger, the Oiltanking Conflicts Committee retained Jefferies as its financial advisor. On November 11, 2014, Jefferies rendered to the Oiltanking Conflicts Committee its oral opinion, subsequently confirmed in writing, that, as of such date and based upon and subject to the various assumptions, considerations, qualifications and limitations set forth in the written opinion, the exchange ratio to be offered to the holders of Oiltanking common units pursuant to the merger agreement was fair, from a financial point of view, to the Oiltanking unaffiliated unitholders. The full text of the written opinion of Jefferies, which sets forth, among other things, the assumptions made, procedures followed, matters considered and limitations on the scope of the review undertaken by Jefferies in rendering its opinion, is attached as Annex B to this proxy statement/prospectus and is incorporated herein by reference in its entirety. The opinion was directed to the Oiltanking Conflicts Committee and addresses only the fairness, from a financial point of view and as of the date of the opinion, to the Oiltanking unaffiliated unitholders, of the exchange ratio to be offered to the holders of Oiltanking common units pursuant to the merger agreement. The opinion does not address any other aspect of the merger and does not constitute a recommendation as to how any holder of Oiltanking common units should vote on the merger or any matter relating thereto.

Certain Relationships; Interests of Certain Persons in the Merger (page 93)

Oiltanking has extensive and ongoing relationships with Enterprise and its affiliates. Enterprise represented 12%, 13%, 29% and 30% of Oiltanking’s revenues during 2011, 2012, 2013 and the nine months ended September 30, 2014, respectively.

Enterprise and EPO, both of which have agreed to vote in favor of the merger and the merger agreement, currently beneficially own approximately 66% of Oiltanking’s outstanding common units. Other than this 66% ownership, the directors, executive officers and other affiliates of Enterprise collectively own or control less than 1% of Oiltanking’s outstanding common units.

Certain current executive officers of Oiltanking GP are current employees of EPCO. A number of EPCO employees who provide services to Oiltanking also provide services to Enterprise, often serving in the same positions. Enterprise GP also has indirect power to cause the appointment or removal of the directors of

Oiltanking GP, an indirect wholly owned subsidiary of Enterprise. Oiltanking has an extensive and ongoing relationship with EPCO, which provides all administrative services to both Enterprise and its subsidiaries, including Oiltanking and its subsidiaries, pursuant to an administrative services agreement.

Further, Oiltanking GP’s directors and executive officers have interests in the merger that may be different from, or in addition to, your interests as a unitholder of Oiltanking, including:

Each of the executive officers and directors of Enterprise GP is currently expected to remain an executive officer or director of Enterprise GP following the merger.

The Merger Agreement (page 66)

The merger agreement is attached to this proxy statement/prospectus as Annex A and is incorporated by reference into this document. You are encouraged to read the merger agreement because it is the legal document that governs the merger.

What Needs to Be Done to Complete the Merger

Enterprise and Oiltanking will complete the merger only if the conditions set forth in the merger agreement are satisfied or, in some cases, waived. The obligations of Enterprise and Oiltanking to complete the merger are subject to, among other things, the following conditions:

Enterprise’s obligation to complete the merger is further subject to the following conditions:

Oiltanking’s obligation to complete the merger is further subject to the following conditions:

Each of Enterprise and Oiltanking (with the consent of the Oiltanking Conflicts Committee and the Oiltanking Board) may choose to complete the merger even though any condition to its obligation has not been satisfied if the necessary unitholder approval has been obtained and the law allows it to do so.

No Solicitation

Oiltanking GP and Oiltanking have agreed that they will not, and they will use their commercially reasonable best efforts to cause their representatives not to, directly or indirectly, initiate, solicit, knowingly encourage or knowingly facilitate any inquiries or the making or submission of any proposal that constitutes, or may reasonably be expected to lead to, an acquisition proposal, or participate in any discussions or negotiations regarding, or furnish to any person any non-public information with respect to, any acquisition proposal, unless the Oiltanking Conflicts Committee, after consultation with its outside legal counsel and financial advisors, determines in its good faith judgment that such acquisition proposal constitutes or is likely to result in a superior proposal and the failure to do so would be inconsistent with its duties under Oiltanking’s partnership agreement and applicable law. Please read “The Merger Agreement — Covenants — No Solicitation; Acquisition Proposals; Change in Recommendation” for more information about what constitutes an acquisition proposal and a superior proposal.

Change in Recommendation

The Oiltanking Conflicts Committee is permitted to withdraw, modify or qualify in any manner adverse to Enterprise its recommendation of the merger agreement and the merger or publicly approve or recommend, or publicly propose to approve or recommend, any acquisition proposal, referred to in this proxy statement/

prospectus as a “change in recommendation,” in certain circumstances. Specifically, if, prior to receipt of Oiltanking unitholder approval, the Oiltanking Conflicts Committee concludes in its good faith judgment, after consultation with its outside legal counsel and financial advisors, that a failure to change its recommendation would be inconsistent with its duties under Oiltanking’s partnership agreement and applicable law, the Oiltanking Conflicts Committee may determine to make a change in recommendation.

Termination of the Merger Agreement

Enterprise and Oiltanking can agree to terminate the merger agreement by mutual written consent at any time without completing the merger, even after the Oiltanking unitholders have approved the merger agreement and the merger. In addition, either party may terminate the merger agreement on its own upon written notice to the other without completing the merger if:

Enterprise may terminate the merger agreement at any time if (i) Oiltanking determines not to, or otherwise fails to, hold the Oiltanking special meeting because of a change in recommendation pursuant to the merger agreement, (ii) Oiltanking does not obtain the necessary unitholder approval at the Oiltanking special meeting or (iii) an Oiltanking change in recommendation occurs.

Oiltanking may terminate the merger agreement if (i) Oiltanking determines not to, or otherwise fails to, hold the Oiltanking special meeting because of a change in recommendation pursuant to the merger agreement or (ii) Oiltanking does not obtain the necessary unitholder approval at the Oiltanking special meeting.

The Oiltanking Conflicts Committee, on behalf of Oiltanking, may terminate the merger agreement (i) upon written notice to Enterprise, in the event that an Oiltanking change in recommendation occurs or (ii) at any time prior to the Oiltanking special meeting, if Oiltanking receives an acquisition proposal from a third party, the Oiltanking Conflicts Committee concludes in its good faith judgment that such acquisition proposal constitutes a superior proposal, the Oiltanking Conflicts Committee has made a change in recommendation pursuant to the merger agreement with respect to such superior proposal, Oiltanking has not knowingly and intentionally breached the no solicitation covenants contained in the merger agreement, and the Oiltanking Conflicts Committee concurrently approves, and Oiltanking concurrently enters into, a definitive agreement with respect to such superior proposal.

Material U.S. Federal Income Tax Consequences of the Merger (page 121)

Tax matters associated with the merger are complicated. The U.S. federal income tax consequences of the merger to an Oiltanking public unitholder will depend on such unitholder’s own situation. The tax discussions in this proxy statement/prospectus focus on the U.S. federal income tax consequences generally applicable to individuals who are residents or citizens of the United States that hold their Oiltanking common units as capital assets, and these discussions have only limited application to other unitholders, including those subject to special tax treatment. Oiltanking public unitholders are urged to consult their tax advisors for a full understanding of the U.S. federal, state, local and foreign tax consequences of the merger that will be applicable to them.

Oiltanking expects to receive an opinion from Vinson & Elkins to the effect that no gain or loss should be recognized by the Oiltanking public unitholders to the extent Enterprise common units are received as a result of the merger, other than gain resulting from either (i) any decrease in partnership liabilities pursuant to Section 752

of the Internal Revenue Code, or (ii) any cash received in lieu of any fractional Enterprise common units. Enterprise expects to receive an opinion from Andrews Kurth to the effect that no gain or loss should be recognized by Enterprise unaffiliated unitholders as a result of the merger (other than gain resulting from any decrease in partnership liabilities pursuant to Section 752 of the Internal Revenue Code). Opinions of counsel, however, are subject to certain limitations and are not binding on the Internal Revenue Service, or “IRS,” and no assurance can be given that the IRS would not successfully assert a contrary position regarding the merger and the opinions of counsel.

The U.S. federal income tax consequences described above may not apply to all holders of Enterprise common units and Oiltanking common units. Please read “Material U.S. Federal Income Tax Consequences of the Merger” beginning on page 121 for a more complete discussion of the U.S. federal income tax consequences of the merger.

Other Information Related to the Merger

No Dissenters’ or Appraisal Rights (page 63)

Oiltanking unitholders do not have dissenters’ or appraisal rights under applicable Delaware law or contractual appraisal rights under Oiltanking’s partnership agreement or the merger agreement.

Antitrust and Regulatory Matters (page 63)

The merger is subject to both state and federal antitrust laws. Under the rules applicable to partnerships, no filing is required under the Hart-Scott-Rodino Antitrust Improvements Act of 1976 (the “HSR Act”). However, Enterprise has received an initial inquiry letter relating to its acquisition of Oiltanking GP and existing ownership interests in Oiltanking, and Enterprise or Oiltanking may receive additional inquiries or requests for information concerning the proposed merger and related transactions from the Federal Trade Commission (“FTC”), the Antitrust Division of the Department of Justice (“DOJ”), or individual states, or the FTC or DOJ could take such action under the antitrust laws as it deems necessary or desirable in the public interest.

Listing of Common Units to be Issued in the Merger (page 64)

Enterprise expects to obtain approval to list on the NYSE the Enterprise common units to be issued pursuant to the merger agreement, which approval is a condition to the merger.

Accounting Treatment (page 64)

The proposed merger will be accounted for in accordance with Accounting Standards Codification 810, Consolidations — Overall — Changes in Parent’s Ownership Interest in a Subsidiary, which is referred to as ASC 810. Changes in Enterprise’s ownership interest in Oiltanking, while Enterprise retains its controlling financial interest in Oiltanking, will be accounted for as an equity transaction and no gain or loss will be recognized as a result of the proposed merger. The proposed merger represents Enterprise’s acquisition of the noncontrolling interests in Oiltanking.

Comparison of the Rights of Enterprise and Oiltanking Unitholders (page 105)

Oiltanking unitholders will own Enterprise common units following the completion of the merger, and their rights associated with Enterprise common units will be governed by, in addition to Delaware law, Enterprise’s partnership agreement, which differs in a number of respects from Oiltanking’s partnership agreement.

Pending Litigation (page 64)

On November 20, 2014, Matthew Ellis, a purported unitholder of Oiltanking, filed a complaint in the United States District Court of the Southern District of Texas, Houston Division, as a putative class action on behalf of the unitholders of Oiltanking, captioned Matthew Ellis v. Bryan Bulawa, William Ordemann, Robert D. Sanders, Michael C. Smith, Gregory C. King, D. Mark Leland, Thomas M. Hart III, Oiltanking Partners, L.P., OTLP GP LLC, Enterprise Products Partners L.P., Enterprise Products Holdings LLC, Enterprise Products Operating LLC and EPOT MergerCo LLC, Civil Action No. 4:14-cv-3343. On December 12, 2014, the plaintiff filed a motion to dismiss without prejudice and the court issued a notice of dismissal of this case.

On December 23, 2014, Mathew Ellis and Chaile Steinberg, purported unitholders of Oiltanking, filed a complaint in the Court of Chancery of the State of Delaware, as a putative class action on behalf of the Oiltanking unitholders, captioned Mathew Ellis and Chaile Steinberg v. OTLP GP, LLC, Oiltanking Holding Americas, Inc., Oiltanking GMBH, Marquard & Bahls AG, Kenneth F. Owen, Christian Flach, Enterprise Products Partners L.P. and Enterprise Products Holdings LLC, Case No. 10495. This new Ellis complaint alleges, among other things, that Oiltanking GP breached the implied covenant of good faith and fair dealing, that Oiltanking GP has breached the Oiltanking partnership agreement, and that other defendants have aided and abetted Oiltanking GP’s breach of the Oiltanking partnership agreement or contractual duty of good faith thereunder. The plaintiffs seek to (i) enjoin the special meeting to vote on the merger proposal unless it is subjected to an unaffiliated vote and (ii) in the event the merger approval is not compelled to be subject to an unaffiliated vote, an award of money damages.

While Enterprise and Oiltanking cannot predict the outcome of this lawsuit or any other lawsuits that might be filed subsequent to the date of the filing of this proxy statement/prospectus, nor can Enterprise and Oiltanking predict the amount of time and expense that will be required to resolve this lawsuit or any other lawsuits, Enterprise, Oiltanking and the other defendants named in this lawsuit intend to defend vigorously against this and any other actions.

Summary of Risk Factors (page 31)

You should consider carefully all of the risk factors together with all of the other information included in this proxy statement/prospectus before deciding how to vote. The risks related to the merger and the related transactions, Enterprise’s business, Enterprise common units and risks resulting from Enterprise’s organizational structure are described under the caption “Risk Factors” beginning on page 31 of this proxy statement/prospectus. Some of these risks include, but are not limited to, those described below:

Organizational Chart

Before the Merger

The following diagram depicts a simplified organizational structure of Enterprise and Oiltanking as of December 31, 2014 before the consummation of the merger and the other transactions contemplated by the merger agreement.

After the Merger

The following diagram depicts a simplified organizational structure of Enterprise and Oiltanking immediately after giving effect to the merger and the other transactions contemplated by the merger agreement, as well as an anticipated contribution of resulting limited partner interests in the merger by Enterprise to EPO.

SUMMARY HISTORICAL AND PRO FORMA FINANCIAL AND OPERATING INFORMATION OF

ENTERPRISE AND OILTANKING

The following tables set forth, for the periods and at the dates indicated, summary historical financial and operating information for Enterprise, summary historical financial information for Oiltanking and summary unaudited pro forma financial information for Enterprise after giving effect to the proposed merger with Oiltanking. The summary historical financial data as of and for each of the years ended December 31, 2011, 2012 and 2013 are derived from and should be read in conjunction with the audited financial statements and accompanying footnotes of Enterprise and Oiltanking, respectively. The summary historical financial data as of and for the nine-month periods ended September 30, 2014 and 2013 are derived from and should be read in conjunction with the unaudited financial statements and accompanying footnotes of Enterprise and Oiltanking, respectively.

Enterprise’s and Oiltanking’s consolidated balance sheets as of December 31, 2012 and 2013 and as of September 30, 2014, and the related statements of consolidated operations, comprehensive income, cash flows and equity for each of the three years in the period ended December 31, 2013 and the nine months ended September 30, 2014 and 2013 are incorporated by reference into this proxy statement/prospectus from Enterprise’s and Oiltanking’s respective Annual Reports on Form 10-K for the year ended December 31, 2013, and their Quarterly Reports on Form 10-Q for the three months ended September 30, 2014.

The summary unaudited pro forma condensed consolidated financial statements of Enterprise show the pro forma effect of Enterprise’s proposed merger with Oiltanking. For a complete discussion of the pro forma adjustments underlying the amounts in the table on the following page, please read “Unaudited Pro Forma Condensed Consolidated Financial Statements” beginning on page F-2 of this proxy statement/prospectus.

Upon Enterprise’s completion of the acquisition of Oiltanking GP and related incentive distribution rights, 15,899,802 Oiltanking common units and 38,899,802 Oiltanking subordinated units on October 1, 2014, Oiltanking became a consolidated subsidiary of Enterprise for financial accounting and reporting purposes. The proposed merger will be accounted for in accordance with Accounting Standards Codification 810, Consolidations — Overall — Changes in Parent’s Ownership Interest in a Subsidiary, which is referred to as ASC 810. Changes in Enterprise’s ownership interest in Oiltanking, while Enterprise retains its controlling financial interest in Oiltanking, will be accounted for as an equity transaction and no gain or loss will be recognized as a result of the proposed merger. The proposed merger represents Enterprise’s acquisition of the noncontrolling interests in Oiltanking.

The unaudited pro forma condensed consolidated financial statements have been prepared to assist in the analysis of financial effects of the proposed merger between Enterprise and Oiltanking. The unaudited pro forma condensed statements of consolidated operations for the year ended December 31, 2013 and the nine months ended September 30, 2014 assume the proposed merger-related transactions occurred on January 1, 2013. The unaudited pro forma condensed consolidated balance sheet assumes the proposed merger-related transactions occurred on September 30, 2014. The unaudited pro forma condensed consolidated financial statements are based upon assumptions that Enterprise and Oiltanking believe are reasonable under the circumstances, and are intended for informational purposes only. They are not necessarily indicative of the financial results that would have occurred if the transactions described herein had taken place on the dates indicated, nor are they indicative of the future consolidated results of the combined entity.

Enterprise’s non-generally accepted accounting principles, or non-GAAP, financial measures of gross operating margin and Adjusted EBITDA are presented in the summary historical and pro forma financial information. Please read “— Non-GAAP Financial Measures,” which provides the necessary explanations for these non-GAAP financial measures and reconciliations to their most closely related GAAP financial measures.

For information regarding the effect of the proposed merger on pro forma distributions to Oiltanking unitholders, please read “Comparative Per Unit Information.” For additional financial information, please read “Selected Financial Data and Pro Forma Information of Enterprise and Oiltanking” on page 87.

Enterprise and Oiltanking completed two-for-one common unit splits of their limited partner units on August 21, 2014 and July 14, 2014, respectively. All references to units outstanding and per unit amounts in this proxy statement/prospectus for each company have been adjusted to give effect to the respective unit splits.

Summary Historical and Pro Forma Financial Information of Enterprise

Summary Historical Operating Information of Enterprise

As used in the table above, the following industry abbreviations mean the following:

Enterprise’s consolidated historical operating data does not include Oiltanking’s assets and operations. For Oiltanking’s consolidated historical operating data, please read the Oiltanking reports filed with the SEC and incorporated by reference into this proxy statement/prospectus.

Summary Historical Financial Information of Oiltanking

Non-GAAP Financial Measures

This section provides reconciliations of Enterprise’s and Oiltanking’s non-GAAP financial measures included in this proxy statement/prospectus to their most directly comparable financial measures calculated and presented in accordance with accounting principles generally accepted in the U.S., or “GAAP.” Within this document, Enterprise and Oiltanking both present the non-GAAP financial measure of gross operating margin

and Enterprise also presents the non-GAAP financial measure of Adjusted EBITDA. These non-GAAP financial measures should not be considered as an alternative to GAAP measures such as net income, operating income, net cash flows provided by operating activities or any other measure of liquidity or financial performance calculated and presented in accordance with GAAP. These non-GAAP financial measures may not be comparable to similarly titled measures of other companies because they may not calculate such measures in the same manner as Enterprise or Oiltanking do.

Gross Operating Margin

We evaluate segment performance based on the non-GAAP financial measure of gross operating margin. Total segment gross operating margin is an important performance measure of the core profitability of our operations. This measure forms the basis of our internal financial reporting and is used by management in deciding how to allocate capital resources among business segments. We believe that investors benefit from having access to the same financial measures that management uses in evaluating segment results. The GAAP measure most directly comparable to total segment gross operating margin is operating income. The non-GAAP financial measure of total segment gross operating margin should not be considered an alternative to GAAP operating income. Gross operating margin is presented on a 100% basis before the allocation of earnings to noncontrolling interests.

The following table presents a reconciliation of Enterprise’s GAAP operating income to its non-GAAP financial measure of total gross operating margin, on a historical and pro forma basis, as applicable for each of the periods indicated:

The following table presents a reconciliation of Oiltanking’s GAAP operating income to its non-GAAP financial measure of total gross operating margin, on a historical basis, as applicable for each of the periods indicated:

Adjusted EBITDA

Adjusted EBITDA is commonly used as a supplemental financial measure by management and by external users of Enterprise’s financial statements, such as investors, commercial banks, research analysts and rating agencies, to assess: (i) the financial performance of Enterprise’s assets without regard to financing methods, capital structures or historical cost basis; (ii) the ability of Enterprise’s assets to generate cash sufficient to pay interest cost and support its indebtedness; and (iii) the viability of projects and the overall rates of return on alternative investment opportunities. The GAAP measure most directly comparable to Adjusted EBITDA is net cash flows provided by operating activities.

The following table presents Enterprise’s calculation of Adjusted EBITDA (unaudited) on a historical and pro forma basis and a reconciliation of Enterprise’s non-GAAP financial measure of Adjusted EBITDA to its GAAP financial measure of net cash flows provided by operating activities on a historical basis.

COMPARATIVE PER UNIT INFORMATION

The following table sets forth (i) historical per unit information of Enterprise, (ii) the unaudited pro forma per unit information of Enterprise after giving pro forma effect to the proposed merger and the transactions contemplated thereby, including Enterprise’s issuance of 1.30 Enterprise common units for each outstanding Oiltanking common unit (other than Oiltanking common units owned by EPO), and (iii) the historical and equivalent pro forma per unit information for Oiltanking.

You should read this information in conjunction with (i) the summary historical financial information included elsewhere in this proxy statement/prospectus, (ii) the historical consolidated financial statements of Oiltanking and Enterprise and related notes that are incorporated by reference in this proxy statement/prospectus and (iii) the “Unaudited Pro Forma Condensed Consolidated Financial Statements” and related notes included elsewhere in this proxy statement/prospectus. The unaudited pro forma per unit information does not purport to represent what the actual results of operations of Oiltanking and Enterprise would have been had the proposed merger been completed in another period or to project Oiltanking’s and Enterprise’s results of operations that may be achieved if the proposed merger is completed.

In calculating the historical “book value per common unit” amounts for Oiltanking presented in the following tables, Oiltanking’s common and subordinated units were treated as one class of units. Oiltanking’s subordinated units owned by Enterprise converted to common units on a one-for-one basis on November 17, 2014.

MARKET PRICES AND DISTRIBUTION INFORMATION

Enterprise common units are traded on the NYSE under the ticker symbol “EPD,” and the Oiltanking common units are traded on the NYSE under the ticker symbol “OILT.” The following table sets forth, for the periods indicated, the range of high and low sales prices per unit for Enterprise common units and Oiltanking common units, on the NYSE composite tape, as well as information concerning quarterly cash distributions declared and paid with respect to each period. Oiltanking’s common units began trading on July 14, 2011, at an initial offering price of $10.75 per unit (split adjusted). Prior to July 14, 2011, Oiltanking’s equity securities were not listed on any exchange and there was no public market for its common units.

Enterprise and Oiltanking completed two-for-one common unit splits of their limited partner units on August 21, 2014 and July 14, 2014, respectively. All references to sales prices and distributions per unit in the following table have been adjusted to give effect to the respective unit splits. The sales prices are as reported in published financial sources, after giving effect to the unit splits.