It’s world wide demand.
Of which supply seems to have no problem in meeting.
The oil companies know the true value of a barrel of oil. Whenever a new oil field is discovered or new innovations in drilling are perfected, the oil companies do a cost/benefit analysis to determine where and how to drill. If it will be profiable they drill. If not they don't. They are currently basing their R&D and exploration decisions on $50 per barrel oil. They know that $140 oil could go away with the stroke of a pen.
Just now in the news is a report that according to analysts crude oil is used as a hedge against the value of the dollar (Fox News) and as the dollar goes down the price of crude goes up. That does not sound to me as if supply vs demand is driving the price of crude or fuel, but it’s the speculators that are driving this increase. So, now, I’ve heard around a half dozen or more different causes for why the price of crude/fuel has shot up so much so fast - who is telling the truth? I’m guessing that no one is.