Oil production and consumption, and helped it improve it's forex reserves
In the way most countries (and their wananchi) view such things, forex reserves have little significance to the USA, keeping in mind that
most folks want to hold their foreign reserves in US dollars and use that currency for the big trades. US foreign reserves since 1960 have barely tripled and the USA probably ranks something like No. 20 worldwide in such things.
That is why China has something like $4 trillion worth of foreign reserves---majority in dollars---whereas the USA has only $150 billion (less than Singapore, Mexico, Algeria, and the like).
That's how it is when your currency is king and accepted everywhere.