Gas Type by Car: Regular, Premium, Diesel or E85 / Cadillac / XT6Cadillac XT6 Gas type by year YearGas type2025Depends on engine: premium or regular2024Depends on engine: premium or regular2023Depends on engine: premium or regular2022Depends on engine: premium or regular2021Depends on engine: premium or regular2020Regular Source: U.S. EPA / DOE fuel economy data (fueleconomy.gov).