Vehicle emissions have been measured and the results statistically evaluated for a vehicle test fleet consisting of four Escorts and four Explorers using both a fully formulated durability fuel doped with methylcyclopentadienyl manganese tricarbonyl (MMT) at 1/32 gram Mn/gallon and the same fully formulated durability fuel without the MMT. The fleet was divided in half -- half with MMT and half without MMT doped fuel. This report covers emission measurement results at 5,000; 15,000; 50,000 and 100,000 miles of exposure to MMT doped fuel. A modified paired t-test is used to analyze the emission data obtained from all the fleet vehicles. The statistical evaluation of both feedgas and tailpipe emissions indicate that the use of MMT is detrimental to emissions of HC at the 15,000 mile; 50,000 mile and 100,000 mile levels of MMT exposure. As mileage is accumulated, the pronounced the effect on HC by the fuel additive MMT. Although the effect of MMT on HC emissions is very clearly detrimental, conversely, there is no clear significant difference in CO and NOx levels between those vehicles operated on 1/32 gram Mn/gallon MMT and those vehicles operated on clear fully formulated durability fuel. Particulate emissions to 100,000 miles are described in companion papers[3,8]. The physical and chemical characterization, as well as the final emission results, indicate a detrimental effect by the combustion product of MMT, Mn3O4, on emission components following 100,000 miles exposure to 1/32 gram Mn/gallon MMT doped fuel.