Eric Margolis wrote a great column in the Toronto Sun about why the United States invaded Iraq and Afghanistan. He also mentioned that four major western oil companies, Exxon Mobil, Shell, BP, and Total will be signing a US brokered no-bid contracts to begin exploiting Iraq's oil fields. These same companies were expelled from Iraq when Saddam Hussein nationalized the Iraqi oil industry. He also wrote that the US needs Afghanistan through which to build a pipeline from the oil rich states of Turkmenistan, Uzbekistan and Kazakstan to Pakistan. This oil will help feed the SUVs in America.
I will add that if the US were not leading the oil development and pipelines, Russia and/or China could. If Russia were ever to make an oil development and pipeline agreement with Iran and Azerbaijan, the US could go to war with Iran by using the pretext of Iran exporting Islamic extremism in the Middle East.