Vehicles with catalytic converters or oxygen sensors must use ONLY UNLEADED FUEL, which will reduce exhaust emissions and keep spark plug fouling to a minimum.
This vehicle will perform best with fuel listed in the table.

* U.S. federal law requires that octane ratings be posted on gasoline station pumps.
Fuel with a rating lower than 87 octane (91 RON) will negatively affect the emission control system performance and could also cause engine knocking and serious engine damage.
CAUTION
Leaded fuel is harmful to the catalytic converter and oxygen sensors and will lead to deterioration of the emission control system and or failures.
Gasoline blended with oxygenates such as alcohol or ether compounds are generally referred to as oxygenated fuels. The common gasoline blend that can be used with your vehicle is ethanol blended at no more than 10 %. Gasoline containing alcohol, such as ethanol or methanol, may be marketed under the name "Gasohol".
Vehicle damage and drivability problems resulting from the use of the following may not be covered by the warranty.
Emission Control SystemMazda 6 Owners Manual: Recording of Vehicle Data
This vehicle is equipped with a computer which records the following main vehicle
data related to vehicle controls, operation, and other driving conditions.
Recorded data
Vehicle conditions such as engine speed and vehicle speed
Driving operation conditions such as accelerator and brake ped ...
Mazda 6 Owners Manual: Compression pressure
COMPRESSION INSPECTION
Warning
Hot engines and oil can cause severe burns. Be careful not to burn
yourself during removal/installation of each component.
1. Verify that the battery is fully charged.
Recharge it if necessary. (See BATTERY INSPECTION.)
2. Warm up the engine to the no ...