For many years, governments have driven the improvement of fuel economy in transportation through tightening legislation. This effort has focused on passenger cars, but is increasingly concerned with heavy-duty vehicles (HDV). The combination of this regulatory focus with the ever present desire for low cost of ownership in commercial vehicles is giving increased pressure to deliver more fuel efficiency from the lubricants.In order to deliver improved fuel efficiency, suitable test methodology is needed to give repeatable discriminatory results that not only help in the advance of technology, but can also highlight the magnitude of the benefit expected in real-world applications. Typical on-road driving has significant variation in fuel consumption due to driver inconsistency, changes in rolling resistance and changeable ambient conditions. In order to avoid the effect of such variables, current practices, such as the EPA SmartWay™ methodologies typically utilize gravimetric measurement of removable fuel tanks or more recently the possibility of using Portable Emissions Measuring Systems (PEMS) over a set cycle.These methods do still have significant variability inherent within them, and, therefore an alternative methodology has been developed using Brake Specific Fuel Consumption (BSFC) in an operating vehicle in order to measure fuel consumption in a more repeatable manner. This paper describes the development process that allows this measurement to be undertaken on a vehicle being driven over a set cycle and discusses benefits relative to current methodologies.