In a recent EPA experiment, fuel consumption data was obtained by both the carbon balance method and the fuel flow method. This report was prepared to describe and compare the two methods of measurements. EPA fuel economy measurements are currently obtained by the carbon balance method. Fuel consumption can also be measured by several other methods such as volumetric, fuel flow meters, or gravimetric methods. Accurate comparison between methods must be done statistically and requires a large data base. A recent EPA program which investigated the accuracy of the dynamometer simulation of the speed of a vehicle consisted of numerous repetitive steady state dynamometer tests. This program provided an opportunity to obtain sufficient fuel consumption measurements by both methods for the statistical analysis necessary to detect any difference between the methods.