In Brazil, gasoline boats are mostly equipped with imported engines. These engines are not prepared to gasoline with high ethanol content. CENPES (PETROBRAS Research and Development Center) has large experience in automotive engines and vehicles testing for fuels development. However, gasoline marine engines need infrastructure, methodologies, and equipments different from those typically used in automotive testing. This work describes infrastructure and methodologies developed by CENPES to assess fuels performance in an outboard engine, running at water tank. It also studies the influence of gasoline formulations with different ethanol contents in this kind of engine performance. Additionally, it was performed an endurance test using a gasoline formulation with 10%vol. ethanol.