While each Lexus model differs in requirements as to what octane gas is recommended, nearly all models recommend only premium fuel be used. This ensures optimal smoothness of idle, acceleration and overall power.
Interestingly, many Lexus models are based on shared platforms with Toyota equivalents. The Lexus GX and Toyota 4Runner share many similarities, but only the Lexus recommends premium fuel, while the 4Runner takes 87-octane. Lexus recommends that no lower than 91-octane fuel be used in nearly all of its cars, with the ES being a notable exception. The company does offer insight into what occurs if you use regular fuel: lower power performance. The difference in fuel economy, however, is almost immeasurable. Each model has a full list of specifications and recommended octane gas on the company's homepage, Lexus.com