I switched to Amsoil about 1,000 miles and a little over a month ago and will not go back to regular oil. I like amsoil and it does increase gas mileage it did mine by 3 mpg now I get 33 instead of 28-30mpg. I know it sounds little wacky but I know I do get a lot better mileage on gas with the Amsoil then I have anything else.
2002 Chevy Cavalier Coupe 2200 SFI 5SPD Manual with 91450 miles.
Oil changed: 89616 miles with Amsoil 5w30 Signature Series and Amsoil oil filter.