I use Costco 99, Doug at mrc tested the fuel out on his dyno with my car. He first ran Costco 99 which I had in the tank for weeks, then drained my tank out and ran Tesco 99, it made the exact same power with no difference. A day before he mapped 2 rs6 c7’s, 1 with Tesco 99 and the other with Costco 99. They made the same power, He said it’s the same fuel!!!! Sent from my iPhone using Tapatalk