amsoil is the only company i know of that says you can go 1 year or 10,000 miles before changing it, we go a hole year on it, some of the forklifts at my dads work have had amsoil in them for over two years, and when you pull the dipstick out it is still clean, they are run on propane so they do burn cleaner but normally they were changed once a year with mobile one that came out dirty,last week my brother just pulled the bearings out of one of the semis at my dads work that had over 270,000 miles on it with amsoil since being rebuilt a few years ago, the bearings came out with very little wear, about a month ago he pulled the bearings out of another one with over 300,000 miles on it that used the shell 15w40, the bearings had a good amount of wear.