KiF oil works like this: you pay an amount of oil for your action when you start your impulse. The cost depends on major power, action type and year, and can be read from a table. So you do not pay "on use" in the sense you seem to imply.
There is also an option, where you pay 1/10 of oil per oil dependent unit (first free), bounded by the cost from the table. This lets you get a "cheap" impulse if you want certain action limits but dont use your oil dependent units. Since you usually have one or two big impulses and then some ~2/10 impulses until the turn ends, this dramatically cuts down overall oil cost. In any case, oil cost doesn't depend on performance anymore, and you don't have to spend 30m of book-keeping in 44+ at eot.
Allies have enough oil but need to transport it home (UK). US can dump 5 oil per turn to Canada after USE 15. This takes care of at least 1naval+1combined, meaning US and CW effectively never have oil problems. Oil in the UK is only relevant to mitigate bad turns on the supply lines.
Axis initially has barely enough oil to keep the beast running, and that is historically correct. Esp. for Japan, but Germany also basically consumed all of its (inlc. Romania's) strategic reserves at the point they declared war on the USSR.
“WiF is like sex: sure, it may give some practical results, but that's not why we do it.”
- Richard P. Feynman, 'WiF, Sex, and the Dual Slit Experiment'.