Andrew links to this map, observing it's "one reason we're not leaving Iraq." Ezra remarks that it "helps explain, for one thing, why the Middle East always dominates the foreign policy agenda." It is, however, worth being precise about this. One dove's "it's all about the oil" complaint is another hawk's "we need to keep invading these countries because our economy depends on it."
One observation is that the high concentration of oil in the Middle East makes the region unusually war-prone. Brazilians wouldn't really gain very much from having their government conquer Surinam. But Saddam Hussein or any other Iraqi dictator stood to gain a lot from controlling the Gulf States like Kuwait, Saudi Arabia, Qatar, and the UAE where the population is low but the oil wealth is high. Meanwhile, a country like Iraq or Iran that has a sizable population plus a ton of oil is in a position to build a pretty large military establishment. Hence the Gulf War-era worry that if Saddam was allowed to conquer Kuwait, he'd move on into Saudi Arabia and the rest of the Gulf, thus putting together a country with truly enormous oil revenues and an enormous amount of market power. That's why we stepped in as leaders of an international coalition aimed at rolling back his conquest.
At the end of the day, though, helping small countries resist conquest by larger countries is a perfectly sound principle to uphold. It's true that we might well not have been so eager to save Kuwait had it not had the oil, but it's also unlikely that anyone would have wanted to conquer Kuwait had it not had the oil. Meanwhile, it's one thing to help small countries avoid conquest and thus try to prevent someone like Saddam from gaining hegemony over the whole region. It's another thing to say that we should start conquering countries in order to establish our own hegemony.