A method for lubrication by supplying a liquid lubricant to moving metal parts, more than fifty percent by weight of the liquid lubricant being a triglyceride vegetable oil having a saturated fatty acid content of less than nine percent by weight of the triglyceride vegetable oil and a polyunsaturated fatty acid content of more than seventy percent by weight of the triglyceride vegetable oil, the triglyceride vegetable oil having an American Petroleum Institute Thermo-Oxidation Engine Oil Simulation Test rod residue weight of less than thirty five milligrams and a pour point of less than minus twenty degrees Celsius.