There’s a running refinery in several of the films that is a stronghold for a clan usually. It’s better than the Walking Dead Tv show having cars run for years after industry shuts down , or they siphon gas from some rusted piece of junk.
That is a good question, maybe they had some reserve of local supplies like those cylindrical tanks we see near most refineries in the East Bay or East Texas, and the usage would be pretty low because there's only the clan cars and trading to think about, also, Australia does have some petroleum reserves so we could pretend they were near some of the last active wells. :)
