[glam_100]

The price of derivatives are supposed to be the same as the underlying on expiration due to arbitrage. However they can still be slightly off because arbitrage is not always efficient. It could be the price difference is so small that it doesn't cover execution cost and interest, or it could be the last second ticks that came in right before end of trading hours that creates the discrepancy. The point is that price between derivatives and underlyings do not have to be the same on expiration. They're very close only because arbitrager "pushes" the two together as they near expiration.