Interesting, I ran what was in it when I bought it for about 5K miles, then threw in Mobil 1 Euro, and I've done changes of about 5000-7500 miles since with only that oil. I didn't really notice much of a mileage difference. Highest I've ever seen was 33.5 calculated at the pump (35 on the dash) after doing only highway in northern Michigan over the summer, and a good 100 miles of that was absolutely ROMPING on it flowing with people on the highway doing 90-110. Normally, I'm doing 70 up and down 290/53, and a bit of around the burbs off the highway, reads anywhere from 31-32, but usually between 29-30 calculated. Lowest I've ever seen was 27 when I was doing nothing but driving around town.