Frankly, it's hard to know for sure. But it seems unlikely it was exclusively, or even primarily, for the reasons officially stated. See, for example

http://en.wikipedia.org/wiki/Rationale_for_the_Iraq_War#Oil_...

"In April 2001, President George W. Bush's Cabinet agreed to use military intervention in Iraq because it was considered a destabilizing influence to the flow of oil to international markets from the Middle East."