The authors made a high performance disk machine to clarify traction characteristics of lubricating oils, and succeeded in obtaining the traction coefficient curves of the typical lubricating oils at appreciably higher pressures than in earlier experiments. By analyzing the traction coefficients obtained in experiments, the authors made empirical equations for calculating traction coefficients. Unknown factors in the equations could be accurately decided by experiments conducted under low/medium pressure conditions where performance of experiments was comparatively easy. Using the equations, it is possible to estimate the traction coefficient curves at high pressure (pmean =2.0 - 2.7 GPa) where performance of experiments is very difficult due to metallic contacts between surface even when test rollers with very smooth surfaces are used.