Describes a method for the determination of the manganese content of automotive gasoline, when the manganese is present as methylcyclopentadienyl manganese tricarbonyl (MMT[R]). The precision of this test method only applies to the determination of manganese in the range of 10 mg/L to 40 mg/L, but higher concentrations can be measured by prior dilution of the gasoline sample with the specified solvent to bring the test portion within the specified range of the method.