Choosing The Right Fuel; Octane Recommendations - Ford 2011 Focus Owner's Manual

Maintenance and Specifications
WARNING: The fuel system may be under pressure. If the fuel
filler cap is venting vapor or if you hear a hissing sound, wait
until it stops before completely removing the fuel filler cap. Otherwise,
fuel may spray out and injure you or others.
WARNING: If you do not use the proper fuel filler cap,
excessive vacuum in the fuel tank may damage the fuel system
or cause the fuel cap to disengage in a collision, which may result in
personal injury.

Choosing the right fuel

Use only UNLEADED fuel or UNLEADED fuel blended with a maximum
of 10% ethanol. Do not use fuel ethanol (E85), diesel, methanol, leaded
fuel or any other fuel. The use of leaded fuel is prohibited by law and
could damage your vehicle.
Your vehicle was not designed to use fuel or fuel additives with metallic
compounds, including manganese-based additives.
Note: Use of any fuel other than those recommended may cause
powertrain damage, a loss of vehicle performance, and repairs may not
be covered under warranty.

Octane recommendations

Your vehicle is designed to use
"Regular" unleaded gasoline with a
pump (R+M)/2 octane rating of 87.
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.
244
2011 Focus (foc)
Owners Guide, 1st Printing
USA (fus)
87
(R+M)/2 METHOD