One poster said it right; Amsoil is a Multi Level Marketing program and that's why it's so expensive. Yes it's great oil, however, the Penzoil ULTRA Platinum is high in detergents that keep your engine clean. It's made of natural gas, an industry first, and is so pure and clear you can hardly see it on your dipstick. A clean engine is a long lasting one. Both oils have very high levels of detergents. Both have very high specs, way higher than most others. Project Farm gives you a great little shootout. The real key is your maintenance schedule. If money grows on trees, go Amsoil. If you work hard for every penny, go Ultra Platinum. If you're the latter, change your oil often yourself. An oil's other job besides lubricate is to suspend harmful particles and take them to the filter. Unfortunately, filters can only do so much because if they filter down lower than about 20 microns they'd block oil flow, pressure, and that's way more damaging. Make oil changes really fast and easy: if you have room, use the Fumoto oil drain plug valve which lets you put a hose on it and pour it straight into jugs. I like the higher-end Purolator 15k-20k mile filters even though I change every 5k miles max, and stick a round neodymium magnet to it to keep iron particles in the filter. No, the manufacturer's spec oils and filters are not great, because of the conflict of interest; they need to meet CAFE fleet mpg numbers and like a 0w-20 oil gives them .5 mpg more it helps them. They also need you to buy new cars often, so do the math. Love your engine and it'll love you back ;)!!