Sniper and Potato, yes valid points, I would never have bought a "short" fill, understand, there are 12? containers here, all show signs of collapsing and less then full, which is what first got my attention when they were sitting on the shelf. I only cracked the plastic cap seal on the one can, to verify the internal foil seal is as it should be, and it is.

If I would suspected that motor oil would/could evaporate, I never would have stockpiled oil, but I'm wondering is this just a synthetic oil issue, as I can't be the first person to witness any motor oil evaporating, but might be the first to stockpile synthetic oil in plastic containers for years to notice the condition, being synthetic is relatively new compared to dino oil, and its a bit more expensive investment, so less likely to be stockpiled.

Regardless, an expensive lesson learned.