Driver behavior is one of the greatest factors determining fuel consumption and, thus, carbon dioxide emissions from a heavy-duty vehicle. The difference in fuel consumption can be up to 30%, depending on the driver. Education, monitoring, and feedback are ways of guiding drivers toward more fuel-efficient driver behavior. An incentive system related to fuel consumption is one way of giving feedback. The greatest challenge facing transportation companies with such incentive systems is fair measurement of the driver's fuel consumption. This paper focuses on that challenge. As a result of this paper, a method for utilizing fuel consumption data in an incentive system has been developed for the case company Tampere City Transport. Measurement of fuel consumption is based on groups, which are formed by runs with similar vehicles, routes, and time of day. The individual driver's average fuel consumption in a specific group is then compared with the average fuel consumption of all drivers in that specific group.