Judging the technical and/or economical performance of cargo vessels is important but not always clear. It is essential when chartering vessels, buying second hand vessels or designing a vessel. However it is not always that transparant, because the performance of a vessel depends on many characteristics and not unimportant, the purpose of the vessel, the specific trade and planned sailing pattern. This paper attempts to give an answer on questions like how can I judge the fuel consumption of a specific vessel, what is its technical and financial performance in a certain trade in comparison to other vessels and why. The paper gives a methodology how to approach these questions in a systematic way. The methodology will be explained by applying it to Roll on Roll of vessels with examples.