I not convinced oil is that big a deal these days. The US kind of owns huge swathes of the world economy - tech - facebook, google apple etc, fast food and drink - coke, pepsi, McD, places to stay - Hilton, Sheraton, airbnb and so on. Typed in Bangkok on an Apple while drinking coffee paid for on MasterCard while waiting to fly on a Boeing.

So people will lend to the US as it had a lot of income, assets and a reputation for paying. Compare that to the country with the world largest oil reserves, Venezuela.