At a minimum, gasoline should meet ASTM specification D 4814 in the United States or CAN/CGSB-3.5 or 3.511 in Canada. Some gasolines contain an octane-enhancing additive called methylcyclopentadienyl manganese tricarbonyl (MMT).
We recommend against the use of gasolines containing MMT. See Additives for additional information.
Gasoline Octane
California FuelChevrolet Cobalt Owners Manual. Gasoline Octane
If the vehicle has the 2.2L L4 engine (VIN Code 5),
use regular unleaded gasoline with a posted octane
rating of 87 or higher. If the octane rating is less than
87, an audible knocking noise, commonly referred to
as spark knock, might be heard when driving. If this
occurs, use a gasoline rated ...