Looking at options trading activity among components of the S&P 500 index, there is noteworthy activity today in Blackrock Inc (BLK), where a total volume of 2,359 contracts has been traded thus far today, a contract volume which is representative of approximately 235,900 underlying shares (given that every 1 contract represents 100 underlying shares). That number works out to 40.8% of BLK's average daily trading volume over the past month, of 577,720 shares..