If you put regular gas in a luxury car, it will run less efficiently and may damage the engine over time. The reason for this is that luxury cars require higher octane fuel to run properly. Octane is a measure of a fuel's ability to resist knocking or pinging during combustion, and is therefore important in preventing engine damage. Regular gas has an octane rating of 87, while premium gas has a rating of 91-93. Luxury cars typically require premium gas with an octane rating of 92 or higher.