Rusting is oxidation. No oxygen means no rust. In a commercial setting, when piping water around in steel pipes, oxygen is controlled at very low levels and you never see any rust in those pipes. If oxygen is quite low but not quite absent you can sometimes get a nice black rust going instead of the red rust we all worry about. The black oxide layer actually helps prevent ordinary rusting. In a fuel tank I doubt you are ever going to be as low in oxygen as either of those regimes though.
