In the field of engine development there is a trend towards transient engine optimization for the reduction of both exhaust emissions and fuel consumption. This requires the reliable measurement of increasingly small differences in fuel consumption.Gravimetric fuel consumption measuring systems based on a vessel system fulfill this ask with high accuracy. A double-vessel system has been developed to permit measurements during transient test cycles, in which fuel consumption exceeds the capacity of the measuring vessel. In the following paper this system will be introduced. Furthermore, it will be shown that this approach retains all the advantages of a single-vessel system, such as high measuring accuracy, fuel venting or integrated automatic calibration. Finally, the importance of high-precision fuel temperature conditioning for accurate measurement and for the certification of combustion engines will be illustrated.