ABSTRACT Orimulsion “First Generation,” commonly known as Orimulsion®-100, is a commercial boiler fuel presently used at power plants worldwide (e.g., Canada, Denmark, Japan, Italy, Lithuania, and China). This fuel is manufactured by PDVSA-BITOR (PDVSA, Petroleos de Venezuela South America) from the vast bitumen reserves of the Orinoco Belt, Venezuela. Orimulsion® is a liquid fossil fuel made up of 70% bitumen, and 30% water. Orimulsion®-400 is part of the “New Generation” of Orimulsion-type fuels being developed by PDVSA-BITOR; this formulation includes modifications which enhance the fuel's combustion and transport, while continuing to improve its environmental and economic benefits. The characteristics of Orimulsion® fuels are conducive to the conversion to this fuel in any kind of boiler designed to burn Fuel Oil No. 6 or coal. The introduction of this fuel alternative for utility repowering will have a significant impact on power generation worldwide. The environmental fate and effects of Orimulsion®-400 has been studied by several groups of scientists (e.g., Battelle, 1998; Bjornstead et al., 1998; Environment Canada, 1998; Esclapés et al., 7997, 1998; Johnson et al., 1998a), and this paper is an overview of these studies. This presentation includes: chemical and physical properties of the fuel; behavior of bitumen particles in freshwater and seawater; environmental toxicity studies using Orimulsion®-400 and its new surfactant package; and spill prevention and cleanup methods.