I found this comparison of Mobil 1 and Amsoil. The data, though not conclusive, seems to point to Mobil 1 being a better oil. Here are the links:

http://neptune.spacebears.com/....html

http://neptune.spacebears.com/....html

Test methodology:

http://neptune.spacebears.com/....html

 

18k miles on M1! crazy. I did about 7500 miles on royal purple when i had my 04 Ranger 3.0.

Great find mfisher. worth the reading...

now i just wonder how this could vary from one car to the other since engines are different.

i wouldnt risk 18k miles on my civic though. after reading this i'd use M1 for only about 7-8k miles...just to be safe

 

thats the first of many oil comparisons that have m1 over amsoil that i have seen from independent studies. plus i switch out my amsoil every 5k anyways...

 

every oil weight wil be different.
m1 5-30 may be better then 5-30 amsoil
but on the other hand 5-20 amsoil will be better then 5-20 m1. just have to do your research.

 

I agree that most info that I have read points to Amsoil being higher quality than Mobil 1. This is the first real world test that I have seen posted on the web though. The folks performing the test even went back to test Mobil 1 a second time to see if the results were repeatable. Granted, they cut the retest short, but the data still seemed to point to Mobil 1 being a better oil. I think that Amsoil and Mobil 1 are great oils, especially for those of us that do not use extended drain intervals. Anyway, I felt that it was worth posting the link.

 

Amsoil has several different oils in the same weights... I'm not sure what oil that is but IF it is the API certified oil it is their lowest quality oil they make and I could see Mobil1 beating it...

SMo'

 

Most tests you will see about Amsoil being better then Mobil is tests that Amsoil has performed... They even have different pages with different formats and the same info to make you think your reading new stuff...

SMo'

 

The part of the test that I find most interesting is the change in viscosity that took place in the Amsoil. The Amsoil went from 5W-30 to 5W-40 during the test. This resulted in a 17% reduction in fuel economy and increased motor vibration. A 10% increase in fuel economy was recovered once the oil was drained and refilled....

 

Interesting thread, good stuff