One of the things I've done for years when changing my own oil is take a whif of the freshly opened container of oil. It's been interesting to note the differences in odor, especially when it comes to synthetics. One would think the odor of the finished product would be mostly influenced by the base oil blend since that makes up the largest % of the finished product. Does anyone know if that's truly the case? Here are some of my observations about the smell of new oils: Mobil 1 SS smells different from the Tri-Syn formula. The Tri-Syn had a much more "plastic" odor. The SS is hard to describe, sort of sweet and not really a petroleum odor. Rotella T Synthetic has a sweet, plastic-like odor, with just a hint of petroleum. Very different from the Mobil 1. Conoco's Hydroclear has a very distinct petroleum odor. Mobil's Drive Clean has a very distinct petroleum odor. Castrol's Syntec has the most peculiar odor of all. It doesn't smell like oil. It has a VERY sweet odor, more of a chemical than petroleum smell.