This paper describes how a comprehensive oil analysis program is implemented in operations involving off-highway and similar equipment. Oil samples are taken on a routine basis and thoroughly analyzed in a laboratory. Tests are tailored to the equipment being sampled, and individual records are maintained per unit to allow monitoring of trends. Highly qualified data analysts review test results and provide practical maintenance recommendations. The result is an improvement in reliability, reduced downtime, and the direction of repair efforts only when and where necessary.Test significance and interpretation are discussed and exemplary case histories provided.