This study presents the viability of the use of liquified petroleum gases (LPG) dosage systems in order to solve the fuel supply in four-stroke outboard engines in compliance with regulations concerning emissions of immediate application pollutants. Results obtained show an important decrease in specific fuel consumption (nearly 20%) provoking a small power loss (about 5%), with an extra saving when making use of bottled fuel, which does not suffer spills in the bunkers and maintenance operations. Laboratory tests have been carried out on 8 and 15 HP Yamaha outboard engines, obtaining reductions in pollutants (CO, HC and NOx) of 60% and of 95% for each power, respectively. These trials have been contrasted with tests carried out in the Vigo estuary and the river Mino waterways, both located in the South of Galicia (Spain). Copyright (C) 2003 John Wiley Sons, Ltd.