What if instead of using the oil centers for IPC value, what if you somehow came up with a rule about using oil, and depleating your oil resources. This is just an idea in progress, but I thought of it thinking how Germany began to run low on oil towards the end of the war.
Each oil center produces so many thousands of barrels of oil per turn (can be more first in my head though). Each mechanical device can only be purchased if you have enough oil. EX. Iraq produces 40 thousand barrels of oil per turn and Germany controls it, so germany gets 40,000 barrels of oil per turn. However, for each tank on the board, he has to use 1,000 barrels per turn, each airplane, 500 and so on. If he doesn’t have enough oil, he can only move units for which he has enough oil. So say he has 35 tanks (35,000 barrels) and 20 airplanes (10,000 barrels). He would only be able to move a combination of units that equals 40,000 barrels of oil.
The 000 at the end could be cut off for easy adding purposes 40 barrels 1 per tank and soo on. Just an idea but sounds fun.