A used natural gas engine crankcase oil analysis procedure has been assembled to provide practical engine control data for gas engine operators. Originally, this analysis procedure was assembled and used to solve an ashless dispersant lubricant field problem. The analysis procedure, which consists of recognized tests and methods, is also suitable for examining used metallo-detergent or detergent-dispersant lubricants. Data developed by these test methods are consistent, and permit the operator to prepare historical engine charts for additional insight into engine operations and give better correlation between the laboratory evaluation of lubricant and engine observations. By suggesting or predicting the need for engine maintenance, the used oil analysis permits more economical and reliable operation of gas engines.