AbstractIn this study, we evaluate the effect of supplied oil quantity and contact bulk temperature on micro-pitting life using two-roller contact machine. To quantify the failure rate of damaged surfaces of micro-pitting occurrence, the DBR(Dark and Bright Ratio) method was effectively implemented for observing not a sudden occurrence of macro-pitting but the transition of micro-pitting growth. The failure criterion is set as 4% micro-pitting on contact surfaces, which is adopted from precedent researches. The change of surface damaged area was measured by an optical microscope and calculated by the use of dark and bright ratio of test specimen pictures taken by optical microscope. The optimum oil quantity was determined to obtain the minimum oil quantity with no change in bulk temperature despite of increasing the supplied oil quantity. In conclusion, the influence of supplied oil quantity and contact bulk temperature on micro-pitting lifetime and the surface contact strength by the S-N curves of failure rate are quantitatively reported and expressed as empirical formulas.