An

-beam pumped XeCl laser has been operated in mixtures of Ne/Xe/HCl and Ar/Xe/HCl. Careful measurement of energy deposited by the

-beam was made to allow accurate determination of intrinsic medium efficiency. Laser output in neon was found to agree well with the predictions of a kinetics model, and yielded efficiency of 5-6 percent. In an argon diluent, we have found efficiency as high as 8.0 percent.