The present invention relates to a method of determining a lubrication parameter indicative of a lubrication condition of an oil-lubricated rolling element bearing. The method comprises measuring high-frequency structure-borne acoustic emissions generated by asperity contact between rolling contact surfaces of the bearing, to provide a measured signal. The emitted acoustic energy is then extracted from the measured signal and the lubrication parameter is determined from the acoustic energy. The determination is made on the basis of a power-law relation between acoustic energy and the lubrication parameter.