We were trying to find out why our minivan was getting such bad gas mileage. Then I gassed up my car at the same gas station where my wife gasses up the minivan. My car immediatetly started pinging when going up any hills. I think some gas stations are over rating their octane rating. An engine that pings will cause the computer to increase fuel input by lengthening injector pulse. Thus, worse gas mileage. If you hear any ping use a higher octane or go to a different station. I find Arco cheapest gas to be superior to Cheverons low or mid grade.