Shows tank wagon prices in MI, IL, IN, IA, MO, KS, MN and WI. Additional detail is available for Milwaukee . Note that a markup of a few cents would be charged if gasoline was purchased at a filling station. Source: Congressional hearing:, 1923. A corroborating newspaper article dated in 1923 indicates that those who could buy at least 50 gallons could purchase at the wholesale price, generally 3 cents less than retail.