A nationalised oil industry means the oil revenue goes to the people of the nation. If you look at what Norway has done with its oil revenues to improve the standard of living of its people you can see what I mean -- I'm sure Americans would like a free huge pension when they all retire too.

If you let private individuals own the oil -- in America's case if you give them free leases to produce it -- then you get a small group of private individuals who manipulate production to maximise profits, manipulate the government to avoid paying taxes on it, use their monopoly position to charge artificially high prices and thus make artificial profits for generations etc.

Here's a short history of the astounding corruption and outright robbery of oil consumers over generations, huge tax evasion etc. etc. of the US oil companies :

OPEC and Crude Oil