How much did Avgas cost in 1940?
100 octane fuel was the best possible aviation fuel at that time,introduced in April 1940 .By December 1942, production of 100 octane gasoline had risen to 5.5 million gallons/day; by June 1943, it was approaching 10 million gallons/day; and, by VE-Day, May 7,1945, production exceeded 20 million gallons/day. Avgas was introduced near 1970s. And, then it is very difficult to find exact price for that . But, the at that time the price of car fuel and aviation fuel were not very different. So, you can estimate it to be at 10-12 cents/gallon range. One other way to estimate the cost is by using the inflation adjusters, the current price for 100LL is about $5.5 . So, by using this calculator, it would have cost nearly 10 cents/gallon. (In 1940, Dollar and Pound were nearly same in value.) So, the final answer should be about 10 cents/gallon.