The International Maritime Organization (IMO) Marine Environment Protection Committee (MEPC) has gradually strengthened the laws regulating ship exhaust emissions. The majority of ships designed for international voyages and powered by large two-stroke marine diesel engines use heavy fuel oil (HFO), which has the advantage of a low price compared to other types of fuel. However, HFO generates large amounts of harmful exhaust emissions during combustion in a marine diesel engine. In addition, as fuel costs account for a large portion of the expenditure budgets of the shipping companies that operate and manage such ships, fuel cost reduction is of considerable interest to such companies. In this study, two fuel additives, oil-soluble Ca-based and oil-soluble Fe-based organometallic compounds, which can improve the performance of diesel engines, were injected into HFO at fixed concentrations (1/4000 and 1/6000 of the total fuel, respectively), in attempts to reduce fuel consumption and exhaust emissions. For enhanced experimental accuracy and reproducibility, a large two-stroke diesel engine installed in a land-based power plant was used as the test subject. Evaluative tests were conducted for three engine loads (50%, 75%, and 100%). The engine performance (i.e., the fuel consumption rate, maximum combustion pressure, and exhaust gas temperature) and the exhaust emissions (NOx, particulate matter (PM)) were analyzed before and after the fuel additive insertion. (C) 2016 Elsevier Ltd. All rights reserved.