The paper considers the multilevel methods of unsteady gas flow modeling in gas transport systems of arbitrary configuration, i.e., containing internal and external closed loops. Computational modeling relies on a generalized solution to initial boundary value problem for nonlinear partial differential equations with discontinuous coefficients describing the unsteady pressure and flow distribution in the gas transport system. Considered methods are focused on the use of different variants of finite volume (balance), finite-element (variational) and multigrid approximations of generalized solutions of parabolic equations. The number of levels of the hierarchy of calculations determined by the structure of gas transport system. Proposed methods are vital for solutions of the main gas flow control problems for gas transport systems and ready for use with parallel computing application programming interfaces.