Perhaps someone older can correct me if I am wrong, since this is difficult to research: Here in Germany the tax difference between diesel and gasoline was main

Perhaps someone older can correct me if I am wrong, since this is difficult to research: Here in Germany the tax difference between diesel and gasoline was mainly created in 1991. Gasoline prices were increased to pay for German re-unification and diesel prices weren't taxed as much because of "European tax harmonization" -- I'd say this is code for "we want to remain competitive and lower diesel taxes gives our industry a competitive advantage". To be fair, they increased taxation of diesel passenger cars (yearly fee) as well -- just not enough. So nothing intentional. They needed to increase taxes, gasoline was a convenient target because its price was low compared to previous times or something, they didn't want to hurt the (export oriented) industry, so diesel wasn't taxed as much. Individual consumers looked at total cost of ownership of diesel vs. gasoline cars and started buying the diesel one.