With the growing demand for contamination‐free leak detectors, the replacement of the oil‐sealed mechanical pumps has become an important issue. Despite their higher total ultimate pressure (0.010 Torr), the oil‐free pumps retain the pumping speed for helium at pressures less than 1×10−7Torr. This is sufficient in most applications using a turbomolecular pump as the high vacuum pump. Experimental results obtained with a Contra‐Flow leak detector with both mechanical pumps replaced by oil‐free pumps are presented. System stability and helium background levels permit leak rate measurements near 2×10−10atm cc/s.