Octane recommendations

“Regular” unleaded gasoline with a pump (R+M)/2 octane rating of 87 is recommended. Some stations offer fuels posted as “Regular” with an octane rating below 87, particularly in high altitude areas. Fuels with octane levels below 87 are not recommended.

Do not be concerned if your engine sometimes knocks lightly. However, if it knocks heavily under most driving conditions while you are using fuel with the recommended octane rating, see your authorized dealer to prevent any engine damage.
See also:
The Inside
I'm not a fan of all-gray interiors, which seem drab to me — even more so
than all-black designs — but that's what our MKZ had. Getting past my own
preferences, however, let me appreciate a cabin ...
Readiness for Inspection/Maintenance (I/M) testing
Some state/provincial and local governments may have
Inspection/Maintenance (I/M) programs to inspect the emission control
equipment on your vehicle. Failure to pass this inspection could prevent ...
Vehicle storage
If you plan on storing your vehicle for an extended period of time
(30 days or more), refer to the following maintenance recommendations
to ensure your vehicle stays in good operating condition.
...
