Petrodollars are the dollars a country earns by selling oil, especially the big streams of US dollars that oil-exporting countries took in after oil prices jumped in the 1970s, then spent or lent around the world. Though actually, people almost always say it in the plural; one petrodollar is rare unless someone is talking about the whole oil-and-dollar system. It is a newspaper and economics word. It is not the oil itself, and it is not the cash in your pocket after you fill a car.