Looking at options trading activity among components of the S&P 500 index, there is noteworthy activity today in Citigroup Inc (C), where a total volume of 77,772 contracts has been traded thus far today, a contract volume which is representative of approximately 7.8 million underlying shares (given that every 1 contract represents 100 underlying shares). That number works out to 58.6% of C's average daily trading volume over the past month, of 13.3 million shares..