I'm not the brightest person in the world but help me understand shelf life with engine oil. So if I took a vergin oil sample of say Mobil 1 and kept the rest of that quart for 20 years and then took another sample of it the readings would be way different? To the point that the oil would no longer be useable? What exactly goes bad with the oil? Does the additive package seperate from the base stock? I'm just trying to understand this. Been reading on here a few posts about oil that someone has seen and is old stuff and then someone else posts that they wouldn't use it due to its age. If that is the case then the 3 quarts of Penzoil SAE 30 HD that my father has in his garage that he has been useing in the lawn mowers isn't any good anymore since it is over 14 years old. Correct? There has got to be a reason. I understand what shelf life is. Here in the Air Force we have it on the packings and rubber O-rings and other seals we have on hand to use when we rebuild our Central Gear Box's and Jet Fuel Starters that go in the F-15E. They carry a 2 year shelf life and we have to rotate our stock if we don't make it through them in that time frame. But usually that doesn't happen because we use up everything we have in a few months time and order more. Thanks for any and all help with my understanding of this.