I'm sure many people hold the view that he shouldn't pay you, and I'd agree.
I am one of the few friends I have with a car (as most of them live in SF and use public trans) but occasionally when they want to go out for late night bar hopping etc they will hit me up for a ride (as buses stop around midnight). My policy is that I'll help them out no problem, as I'd rather they call for a ride instead of getting a DUI, but I'll ask them for a contribution to my gas bill. My friends have no problem helping out, but it's arranged before hand.
Also, if you consistently give him rides and he never helps out, then of course he will expect it (and for free none the less). I'd say arrange it ahead of time, don't spring it on him after the fact (especially when he didn't even benefit from the ride).
Not to say he wasn't being a douche by initially saying he was at a petrol station to begin with, then he was at a pub, and then you couldn't find him, but still...