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Founded in 1953 in Saint Joseph, Missouri, the company’s name, STP, was derived from “Scientifically Treated Petroleum”.[1] The company entered into the marketplace with one product, STP Oil Treatment.

In 1961, the company was acquired by the Studebaker-Packard Corporation. Studebaker BRIEFLY tied STP into its advertising as an abbreviation for “Studebaker Tested Products”.

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http://en.wikipedia.org/wiki/STP