I don't think AMSOIL buys their base from Mobil. Mobil 1 is a type 3 "refined petro" synthetic and AMSOIL is a type 4 pure synthetic. In addition, this link shows a comparison of Mobil 1 and AMSOIL. The Mobil 1 test is complete and AMSOIL just started so you can not compare long term results. http://neptune.spacebears.com/cars/stories/oil-life.html The study shows there were stark differences from testing on the initial pour from the bottle. So, I don't think they are similar. Also, AMSOIL has a recommended service interval of 25,000 miles or 1 year with a filter chg mid point on their engine oils - Mobil1 does not do this. Both oils meet specific needs and both have strengths and weaknesses.