I agree with what the others have said - use a combo order to sell both at the same time. Managing a short straddle however might be a whole 'nother issue! JJacksET4
I believe OptionsXpress does not charge another commission for the same thing. For example, I have before bought say 10 calls for $1.00 each limit - 6 were filled and the stock moved up somewhat - I modified the rest to $1.05/per and 4 more were filled and I was charged one commission total. That being said, everyone seems to feel OX has some of the highest commissions so oh well JJacksET4
Exchange fees are also a factor in commissions. For options listed only on PHLX, for instance, PHLX charges you .35/contract whether you're adding or removing liquidity. http://individuals.interactivebrokers.com/en/accounts/fees/PHLXoptfee.php?ib_entity=llc