Contrary to what many people think (and what the oil companies would like us to believe), higher grades of gasoline do not contain more energy.Bottom line: use what your car manual says.
Gasoline is rated by octane; generally, regular is 87 octane, mid-grade is 89 octane, and premium is 91 or 93 octane. Octane ratings indicate the gasoline's resistance to pre-ignition.
 "What kind of gasoline should you put in your car? Regular, mid-grade or premium -- here's how to choose the right fuel." By Aaron Gold, About Autos, 9/29/15.