Where does that come from? Were we heavily dependent on Iraq oil? I don't remember Iraq threatening to stop selling it.
Before the American invasion, Iraq was selling its oil to the Chinese and Russian oil companies. After the invasion, the Americans seized all the fields, and distributed them among the US and EU firms, with a few spare ones going to others. Oil was the main reason why the US invaded Iraq. Don't tell me that they were concerned more with some imaginary WMDs.