...that unleaded gasoline was actually around long before the leaded variety? From 1913 to 1923, all gasoline was unleaded. Then in 1923 General Motors discovered tetraethyl lead (TEL), a new product which increased the octane (anti-knock) rating of gasoline. Ethyl Corporation commercialized and marketed TEL, which is why in old movies you sometimes hear gas station attendants asking customers whether they want "ethyl or regular".