As far my knowledge of oil goes, the US had the most, followed by the USSR and then Venenzula ? So after US puts sanctions on Japan for Oil after they occupy IndoChina. Couldn’t they have just got the oil from Venenzula? They were trading with Dutch East Indies for Oil, which can’t be much and certainly Venenzula sees like the better option.
Here is my guess, US would intercept convoys and ask them turn back and they don’t they would be fired upon? But that would be an act of war, something isolationist US would not do.