After regular trading hours, why is the close price sometimes different from the last price, even for American options, which are supposed to trade only 09:30 - 16:00? For stocks, there is after-hours trading, so Last may be different from Close. But for options? For example, right now, ENER 20090717 14.0 PUT is Last 1.25, Close 0.70.
The 'last' price is worthless unless the options are very actively traded. Those 'last' prices may be hours - even days or weeks 'old'. The closing price is <i>either</i> the last trade (when it is relevant) or the mid-point between the bid and ask prices. Mark http://blog.mdwoptions.com