Can the Car use regular or medium grade fuel?

Your vehicle is designed to use “Regular” unleaded gasoline with pump (R+M)/2 octane rating of 87. We do not recommend the use of gasolines labeled as “Regular” that are sold with octane ratings of 86 or lower in high altitude areas.

The Focus SVT requires a minimum grade of 91 octane fuel.

it says that it can only take 91+ and i would onlty use that because it will blow an O2 senser