[citrusybread]

different compositions. what we call "oil" actually ranges through so many configurations you might as well think of it the same way we think of juice. sulfur and other impurities can change the game dramatically.

it's also the reason Alberta's tar sands have few importers, because not everyone is capable of refining it (which leads to Canada having to export it, and import foreign oil).

there are refineries in the US that only work effectively on Russian oil -- and I'm sure there's similar issues elsewhere in the world. they can probably adapt but it's not as uniform as we'd think.