What will happen if you put regular gas in a premium car?

Using regular gas in a premium car designed for high-octane fuel can lead to reduced performance, such as lower horsepower and acceleration. The engine's knock sensors may compensate for the lower octane by retarding ignition timing, which can result in decreased fuel efficiency and potential engine knocking over time. While occasional use of regular gas may not cause immediate damage, consistently using it can lead to long-term issues with engine performance and durability.