Gas Spending

I was complaining the other day about the amount I was spending on gas to some co-workers so I thought I would pull out my gas spending from MS Money. I am not sure whether some of the avg increase since early 2005 is attributed to gas prices or increasing travel. I'd like to see if I can correlate this chart to avg gas prices and see what relationship there is - it may help explain which month's expenses were due to more driving.