Here's one of your reasons, Bowser, from someone who should know.

Col Lawrence Wilkerson (US Army, Ret.) was chief of staff for Colin Powell during the first Bush Administration, when the invasions of Iraq and Afghanistan were carried out.

He believed the best defense against Iran is Iraqi nationalism, their natural enemy in the area. Here is his testimony.

"This kind of nationalism in Iraq is the best defense against Iran.
Not U.S. forces on the ground, unless, of course, your plan is to go on to
Syria or go on to Iran from Afghanistan and from Iraq. And, of course,
that was the plan of George Bush and Dick Cheney, a plan that was put
asunder by the fact that Iraq turned so badly in the years 2004, `05, `06
and `07."

http://www.msnbc.msn.com/id/45685498/ns/msnbc_tv-rachel_maddow_show/

So you see, it wasn't JUST about oil. And now we know why that war was being planned even before 9/11. We knew we would need bases for future wars.