This work presents an extension of a succession-of-states approach based on the pseudosteady-state behavior, originally established for the single-phase flow of a slightly compressible fluid, to simulate the long-time behavior of real gas flow in a closed reservoir. Pseudo-pressure and normalized pseudotime were introduced as a theoretical basis for deriving a linearized form of gas diffusivity equation. The method, which utilizes a combination of a material balance equation and approximation for the pseudopressure drawdown, represents an improvement over previous methods in computational efficiency. Through a series of numerical simulation works and error analysis, the applicability and limitations of the approach were examined with respect to various reservoir and operational parameters. The parameters, which are considered to develop nonlinearities in the gas flow problems, include permeability, pressure, flow rate, and gas properties. Error analysis demonstrates that the permeability and reservoir pressure can affect the results of a succession-of-states approach. The accuracy depends weakly on the flow rate, and is almost independent of specific gravity. From the practical viewpoint, computations indicate that neglecting infinite-acting flow behavior does not introduce serious error in the procedure except for the cases of very low permeabilities.