A Rancimat (PN EN 14214) test on rapeseed oil's fatty acid Me esters (FAME) run under field (8-10) and room (20 degrees C) conditions showed the oxidn. stability to fail in 8 months from 9.2 to 2 and 2.5 hrs., resp. A phenol deriv., 50 ppm, or butylhydroxytoluene, 0.50/6, made a 5% FAME biodiesel keep the 14214 requirements over 8 months with degradation by similar to 30% only (to 6 hrs.).