Lubrication oils carry information about the condition of industrial plants and machines. The multiparameter condition monitoring system fluidFOX from Micro Resonant reliably determines numerous physical properties of the lubricating oil and thus can contribute to the reduction of unplanned downtimes and maintenance costs as part of more effective predictive maintenance. Reliable determination of oil condition based on objective physical quantities provides additional and complementary information to manifold chemical analysis options. In this contribution, we illustrate the working principle and discuss the application in the industrial field with a focus on reliable online oil condition monitoring.