Considering the changes of gas transmission system (hereinafter – GTS) brought about by diversification of gas suppliers, new interconnections with European GTS and implementation of an open electricity market and then an open gas market, a steady-state GTS modelling tool has been developed for future implementation in the risk and resilience analysis and potentially operational planning for different GTS or other purposes. The developed method combines the linearized hydraulic conductivity approach with a technique, derived from a linear electrical circuit analysis and an additional pressure change term for modelling of active non-pipeline elements of GTS. This method also takes into consideration operational limits of compressors and pressure regulators and changes in compressibility factor and gas viscosity based on the gas composition, temperature and pressure. The paper includes part of the results obtained from a validation case study performed for the presented method.