What fuel type does the Buick Enclave require, and can I use E85?

The Enclave requires Regular 87 octane (R+M)/2 or higher unleaded gasoline, and TOP TIER Detergent Gasoline is recommended. Gasoline-ethanol fuel blends greater than E15 (15% ethanol by volume), such as E85, cannot be used in this vehicle. Using gasoline with an octane rating lower than recommended will result in reduced performance and lower fuel economy. (Page 26)