Iraq wasn't invaded for oil because the oil fields are being sold to China and another country. None of the contenders for the contract were American, for that matter. The invasion of Iraq is still certainly one that puzzles me. If anything, it's probably because they have always been a thorn in the US' side. Out of all the Middle Eastern nations, Iraq probably was seen to be the most violent and therefore most dangerous to American interests. Therefore, during the Kuwait invasion, economic sanctions were placed on Iraq
http://en.wikipedia.org/wiki/Iraq_sanctionsThis killed over a million people (mostly children), created nationwide poverty among other things (also spawned the disgusting Food-For-Oil programme). It was predicted that the disgruntled population would overthrow Saddam but 10 years later, he is still in power. Honestly, it's probably them finishing the job.
Russ does indeed have a point. After the collapse of the regime, I read somewhere that IMF had placed more sanctions (which cannot be reversed under even the new government) called Structural Adjustment Programs. This allows private enterprises (foreign, no doubt) to enter and begin working on the virtually destroyed nation. Iraq's market is also open to multinational companies which essentially kills off local businesses and increases the wealth and power of multinational companies. This happens in third world countries as well, but I wouldn't say for sure that this was the primary reason (Besides that, I think the French are the ones working in Iraq but I haven't looked into the Iraq war much)