I almost always buy citco gas (because its usually the least expensive) and for the first 3 tankfulls i was averaging about 51 mpg. My last tank i put in Mobile (always regular) and noticed that my milage has suffered back to about 48 mpg. However the weather has gotten about 15-20 degrees cooler which has an even greater effect on milage, so who knows if its the gas or the cooler weather.