Gasoline with
lead added to it, brought gradually into use during the
1920's and outlawed in the
United States in
1986.
This additive was thought to improve engine performance and provide other benefits, although it was later decided the benefits of leaded gasoline had been overstated - and the health dangers of leaded gasoline ignored.
Although I have found many articles by reputed journalists claiming there were dangers of leaded gasoline maliciously concealed by gasoline companies, there seem to be no allegations of the overpricing of unleaded gasoline by even the harshest critics of these companies.