The subject matter of this paper applies to all industrial, marine and flight combustion gas turbines; however,the focus is on one particular engine, the General Electric LM-2500 in mechanical drive application. Owners and operators of these machines can reduce operating costs and enhance availability and performance by paying close attention to the operating condition of their equipment. By doing so, performance tuning for optimum operating costs can be accomplished. Likewise, condition based, predictive and preventive maintenance efforts will reduce forced outage and maintenance costs to an absolute minimum.Attaining the described goal requires application of operations and maintenance experience, troubleshooting and diagnostic knowhow, and most importantly, precise planning. Technology exists today that will automate most of the repetitious effort required and allow fleetwide benefit through knowledge based, condition monitoring. This paper describes the concepts of this on-line condition monitoring system (DATM4) and its impact on maintenance and operations.