The majority of used luxury sedans use premium unleaded gasoline. However, there are some makes that use regular. Both Lincoln and Cadillac have luxury sedan models (the Cadillac STS and DTS and the Lincoln Town Car), which have engines that do not require premium gasoline, but regular unleaded. While it’s always a good idea to follow the manufacturer’s recommendations, running regular unleaded gasoline in a luxury sedan that calls for premium won’t damage the engine. Performance may decline, but in most cases it’s unnoticeable. For a quick way to compare luxury sedan models and gasoline grades, visit www.fueleconomy.gov and search for cars by market class.
For more info, see The Most Reliable Used Car Models