An oil-life monitoring system includes an engine revolution counter configured to provide an output corresponding to the rotation of a component of an engine, and a controller in communication with the engine revolution counter. The controller is configured to determine the composition/properties of a fuel being combusted by the engine, and select a fuel quality penalty factor from a table, with the fuel quality penalty factor corresponding to the determined composition/properties of the fuel. Additionally, the controller is configured to compute an adjusted revolution count by multiplying the rotations of the component of the engine by the fuel quality penalty factor, and aggregate the adjusted revolution count.