At Overcoming Bias, Robin Hanson discovers he can save money by mixing premium and regular gasoline rather than buying the mid-grade product, and if you buy mid-grade gasoline for your car then you may be able to save money too.
The opportunity to save depends on the relative octane ratings and prices of regular, mid-grade, and premium. Hanson found: “For regular, mid-grade, premium, the $/gal. prices were 1.77, 1.92, 2.02 , while the octane ratings were 87, 89, 93. So the first jump gives you 2 octane points for $0.15, while the second jump gives you 4 octane points for only $0.10. Since mixing gas averages the octane ratings, if you mix 2/3 regular with 1/3 premium, you make your own mid-grade gas for only 1.85, saving 0.07.”
According to this paper “Relative Gasoline Prices: Octanes and Arbitrage,” cited by Hanson, your effective wage rate for the slight bit of extra trouble could be as much as $340/hr. And if you adopt Hanson’s easy-to-do alternating fill-ups approach rather than the analyzed two-part transaction approach in the paper, you can save money without spending any extra time.