What effect does altitude have on a gasoline engine's octane requirement?

At higher altitudes, the air pressure decreases, leading to a lower air density. This results in a thinner air-fuel mixture entering the engine, which can reduce the likelihood of knocking. Consequently, gasoline engines may have a lower octane requirement at altitude compared to sea level, allowing for the use of lower-octane fuel without risking engine performance or damage. However, this effect can vary based on the specific engine design and operating conditions.