A comparative life cycle assessment (LCA) study of three types of base oils used in the manufacture of hydraulic fluids has been carried out, and is reported here. The fluid types investigated are a mineral oil, a synthetic ester, and a rape seed triglyceride oil. The applications chosen for the finished lubricants are in mobile hydraulic systems in forestry operations, some of which are almost 100% total loss applications. The scope and limitations of the LCA model are discussed, and conclusions drawn concerning the application of LCA models as evaluation tools for the development of environmentally adapted lubricants. The methodology used is compatible with the ISO 14000-type industrial standard.