I've been using Unocal 76 gas to all my vehicles and I remember when the money was really tight (Unemployed) few years ago, I used Costco twice to fill up my Suburban and my Ram 1500 (this is before the Boxster and my Benz')...dude, I did save .$25 cents per gallon but it cost me hundreds of dollars to fix the Suburban. Never again will use different brand...Im not saying Costco is a bad gas but just sharing my experience