The charge-state distributions and equilibrium charge states of uranium ( 238 U) and xenon ( 136 Xe) ions at 11 MeV=nucleon were determined using a gas charge stripper. A differential pumping system facilitated the increase of the nitrogen gas thickness up to 1:3 mg=cm 2 , which is sufficient for the most probable charge state to attain equilibrium. The charge states of 238 U attain equilibrium at 56.0, 56.6, and 55.7 in N 2 , Ar, and CO 2 media with thicknesses of 125, 79, and 126 g=cm 2 , respectively, while those of 136 Xe attain equilibrium at 40.5, 40.1, and 40.3 in N 2 , Ar, and CO 2 media with thicknesses of 163, 95, and 139 g=cm 2 , respectively. The equilibrium charge states of 136 Xe are acceptable for acceleration by the subsequent cyclotron. The measured data of 238 U were used to devise an empirical formula for the prediction of the equilibrium charge state in gaseous media over the energy region of 0:01-60 MeV=nucleon. The equilibrium charge state of 136 Xe as predicted by the devised formula is in good agreement with the data.