Within the article an issues of implementing the new kinds of marine diesel fuels into ships’ operation was described taking into account restrictions on the permissible sulphur content introduced by the International Maritime Organization. This is a new situation for ship owners and fuel producers, which forces the necessity to carry out laboratory research tests on especially adapted engine stands. How to elaborate the method enabling quality assessment of the self-ignition engine performance, considered in three categories: energy, emission and reliability, represents the key issue of the organization of such research. In the field of energy research, it is necessary to know the thermal efficiency of the engine as the basic comparative parameter applied in diagnostic analyzes and syntheses of sequentially tested marine diesel fuels. This type of scientific research has been worked out for two years in the Department of Marine and Land Power Plants of the Gdańsk University of Technology, as a part of the statutory activities conducted in cooperation with the Regional Fund for Environmental Protection in Gdansk and the LOTOS Group oil company. This article presents the algorithm and results of thermal efficiency calculations of the Farymann Diesel D10 test engine in the conditions of feeding with various low-sulfur marine diesel fuels: distillation and residual fuels. This parameters stands for one of ten diagnostic measures of the ranking of energy and emission quality of newly manufactured marine diesel fuels being built at the Department.