This is just a cost benefit analysis, any discussion about US motivations in engaging in the Iraq war I would consider out of scope.
Iraq nationalized oil production in 1972 (source). Following the invasion of Iraq in 2003, in 2005 a new constitution was drafted including language considering how oil should be addressed (source), though proposed laws to better specify what this language entails have stalled due to debate on the topic.
My question is, how much money has been gained by US firms from exposure to Iraqi oil markets since that market has opened up, and how much money was spent on the Iraq war? Bonus for elaborating on the economic effects on the US economy from access to the oil, if it is significant.
I'm aware oil is a militarily strategic resource and not purely an economic one, but it is harder to quantify the benefit in this regard.