Gas Type by Car: Regular, Premium, Diesel or E85 / Cadillac / XTSCadillac XTS Gas type by year YearGas type2019Depends on engine: premium or regular2018Depends on engine: premium or regular2017Regular2016Depends on engine: regular or premium2015Regular2014Depends on engine: regular or premium2013Regular Source: U.S. EPA / DOE fuel economy data (fueleconomy.gov).