The use of palm oil as a base stock for an environmentally friendly lubricant for small four-stroke motorcycle engines is investigated. Palm oil was blended with mineral oil at different compositions to the viscosity requirement of commercial lubricant. A liquid additive package was added to improve the viscosity of the lubricant. A blend that meets the viscosity requirement was then chosen for physical and chemical property characterization and subjected to an engine test. The blend consists of 50.6% (wt.) palm oil, 41.6% mineral oil, and 7.8% additive package. The properties evaluated include viscosity, viscosity index, flash point, foaming characteristics, and wear scar. The engine performance and emission tests were carried out with a 125-cc motorcycle on a chassis dynamometer using a Bangkok Driving Cycle. Compared to a mineral-based commercial oil, the palm oil-based lubricant exhibits superior tribological properties, but offers no clear advantage on engine and emission performance. (C) 2010 Elsevier Ltd. All rights reserved.