The charge-state distributions of 238U and 136Xe ions at 11 MeV/nucleon were measured using a gas charge stripper to test whether the charge states in gaseous media were acceptable for acceleration at the RIKEN RI-Beam Factory (RIBF). A differential pumping system facilitated the increase of the N 2 gas thickness to 1.3 mg/cm 2; this is sufficient for the most probable charge state to attain equilibrium. The charge states of 238U 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 μ g / cm 2 , respectively, whereas those of 136Xe attain equilibrium at 40.5, 40.1, and 40.3 in N 2, Ar, CO 2 media with thicknesses of 163, 95, and 139 μ g / cm 2 , respectively. The equilibrium charge states of 136Xe are acceptable for acceleration by the subsequent cyclotron, whereas those of 238U are not acceptable for acceleration without a major remodeling of the accelerator.