I like IL’s rules and I am going to use them with slight modifications.
Germany and Italy will use the oil fields of Romania. I also think that if they can trace a supply path to Venzuela, they would have oil.
Japan needs oil somewhere, give them oil from Russia and the us until certain times of the war , then when they are at war, they must have oil secured or serve penalties.
Penalities would be either moving only half their pieces they require fuel or make them all move a limited range.