The continuous monitoring of the oil condition with sensors is regarded essential, especially in the context of on board application. Due to long distances between engine control room and machinery, the regular “manual” control of crucial oil parameters is not always possible. Therefore, installation of inline or online sensors enables precise permanent monitoring of various oil properties. Through the connection to special data processing and storage unit, the real-time assessment of the oil condition and its quality can be easily conducted. Sensor technology allows direct notification of any changes in the oil condition, and by means of the early warning function an undetected leakage or higher metal friction can be immediately recognized. Thus, effective condition-based maintenance practices can be established. The modular design of the monitoring system makes it suitable for various application areas: main engines, generators, hydraulic systems, steering gears etc.