Drawdown with a constant-surf ace-conditions gas rate into a single well, starting at homogeneous pressure conditions in a cylindrical gas reservoir, is simulated numerically. For radii much larger than the wellbore radius, the pseudopressure solution in the infinite-acting period can be plotted uniquely as a function of a Boltzmann variable s=rb/4tpD' where rD and tpD are dimensionless radius and pseudotime. The nonlinear correction terms in the pseudotime diffusion equation, far from being negligible for drawdown, can become dominant in the infinite-acting period. This confirms an analytical result obtained previously. The correction terms are shown by simulation to be functions of s only for radii much larger than the wellbore radius. Plotted vs. In s, the pseudopressure shows an approximately linear behavior with a slope slightly larger than the usual constant-diffusivity slope. This was predicted by an explicit analytical solution.