Options Expiration Volume

All, I’m trying to get a grasp on the increase in volume on options expiration… Why does it seem there’s always bigger than normal volume on options expiration? If you have a call (SPY 115 as an example) and you want to exercise today, you would buy it at 115 and the seller would sell it at 115, does that volume at a price of 115 reflect in today’s volume or not? If you’re automatically exercised, technically it’s not done until over the weekend, so I think that volume would reflect on Monday.

And I’m talking about volume on the stock side, not the options side–I understand that–people are closing their positions.

Options have the highest gamma the closer to expiration they get. Higher gamma = larger changes in delta. Larger changes in delta = more trading in underlying required to stay delta neutral for delta neutral portfolios (most market makers).

do you think the sec was a buyer of gs put options all week?