I thought options were FIFO but I'm not so sure anymore. The other day I was trading options on C and saw some weird things happen when I would undercut the bid or ask (suddenly tons of options swarming in on the new bid or ask, and then suddenly dissappearing when I took mine out -- usually always the same number). Another thing -- at the end of the day I notice really horrible fills on options that I'm monitoring. I've seen people pay 50% too much or getting a really bad price for a sell -- this is AFTER options trading time -- so WTF? I haven't read anywhere in a book how they jerk people around in the options market -- any ideas / comments?