I had a trip that ended with an ocean crossing, required an RFO. But no RFO was listed. And I mean, NOT LISTED. Not "OPEN" or unassigned, but the trip looked like there was no spot for an RFO. Hmmm. Then we figured it out. They were going to revise it before we left MEM on a 12 day pairing. But of they did that, the captain would have the option to say no thanks, and go into SUB. If they waited till we blocked out, they had him with a trip revision. No reserves were available to cover the trip if he had said no before we left. (I was on reserve...)