Looking at options trading activity among components of the S&P 500 index, there is noteworthy activity today in UnitedHealth Group Inc (UNH), where a total volume of 26,267 contracts has been traded thus far today, a contract volume which is representative of approximately 2.6 million underlying shares (given that every 1 contract represents 100 underlying shares). That number works out to 42.1% of UNH's average daily trading volume over the past month, of 6.2 million shares..