I recently (about 4k ago ..that's recent for me) changed from Mobil 1 to Delvac 1. My wife's Sahara TJ(68,500 at the time of the change) has always gotten between 17 and 17.5 mpg. I check it virtually every fill up. Since the change over I've broken 19+ a few times and am consistantly at 18.5. Now I've used Mobil 1 from around 2500 miles in its various formulas (I had a fondness for the 0w-30 ...but the local stores just don't keep it in stock) but have never observed any fuel economy (I guess it would be hard with using only one oil - you only know if you switch to something different). Just figured that I'd share the observation. I'm going to do a 10k UOA on this jeep with Delvac 1. My last UOA at around 9k the oil was about shot. I wish my Wally World carried the stuff ..but alas ..they only carry the 1300 (yes, only the Delvac 1300 - I even asked the guy stocking the oil).