For optimum mileage the Cadillac XT6 requires premium gas. It's important to note that the MPG figures quoted by Cadillac are based off premium gas. This applies to both the base 4-cylinder turbo motor and the V6 motor for the 2022 XT6. This means the savings you make with the mpg figures of the Cadillac XT6 on both motors may be negated by having to fill the car with premium gas depending on the price at the time.