Looking at options trading activity among components of the S&P 500 index, there is noteworthy activity today in Vistra Corp (VST), where a total volume of 32,953 contracts has been traded thus far today, a contract volume which is representative of approximately 3.3 million underlying shares (given that every 1 contract represents 100 underlying shares). That number works out to 55.4% of VST's average daily trading volume over the past month, of 6.0 million shares..