This inexpensive solution increased fuel consumption. Sales of rotary engine cars suffered because of the oil crisis of 1973 raising the price of gasoline leading to lowering of sales. Toyota discovered that injection of air into the exhaust port zone improved fuel economy reducing emissions. The best results were obtained with holes in the side plates; doing it in the exhaust duct had no noticeable influence. The use of a three-stage catalysts, with air supplied in the middle, as for two-stroke piston engines, also proved beneficial meeting emissions regulations.