So I had hmm.. 1500 or so in single player. Played a shit ton of co-op with my brother this weekend bought tons of oil in his game. When i quick i had around a 2300 gallon max. my save game transferred all the money i made in  co-op (so i have around 50 million now) but my oil didn't transfer over. What's more when I started up the 360 and played some more single player my oil max was at 1300!!!

So I ain't buyin shit for oil in someone elses co-op game ever again. Anyone else have this problem?

Your maximum fuel goes down if one or more of your storage tanks is destroyed at the PMC mansion.  If that is why your max storage went down, then you can buy it again from the faction it was originally purchased (it will still be unlocked).

If that's not the reason, sorry, can't help you.

yeah non of my oil tanks have been destroyed and i couldn't seem to repurchase oil. thanks though.