Abstract: A method for improving varnish control in a mechanical device requiring hydraulic fluids, turbine oils, industrial fluids, circulating oils, or combinations thereof. The method involves supplying the mechanical device with a lubricating composition including a Group III lubricating oil base stock. The Group III lubricating oil base stock has a viscosity from 3.8 to 8.5 mm2/s at 100° C., a viscosity index greater than 120, a sulfur content less than 0.0003 weight percent, and an aromatic hydrocarbon content less than 0.2 weight percent, based on the total weight of the Group III lubricating oil base stock. Varnish reduction properties are improved as compared to varnish reduction properties achieved using a lubricating composition containing a different Group III lubricating oil base stock. The disclosure also provides lubricating compositions used in the method.