I found this looking around and though it was interesting
http://neptune.spacebears.com/cars/stories/mobil1.html
http://neptune.spacebears.com/cars/stories/amsoil.html

Though it was weird that Amsoil oil thickened up

 

I've referencedthat particular website many times in the last few years since it was a long term, independent study. I feel the results give a good deal of info for anyone wondering about Amsoil vs Mobil 1. I used to be an Amsoil dealer myself, but the constant price hikes coupled with this independent test convinced me Mobil 1 was the way to go......

Amsoil will quote test results that favor it's own oil all the time. The thing is, the lab that did the testing is on the Amsoil payroll!!!

Dusty