This paper illustrates by example how a method of optimisation used in the electrical-engineering field is extended and applied to that of gas engineering. This approach of optimising a general gas system is formlated as a general nonlinear programming problem. All the system parameters are expressed in mathematical representation. The usage of natural gas is also included. An iterative approach based on the Lagrangian-multipliers method with penalty functions for the inequality constraints is presented as the method of solution. A small sample system which consists of the essential parameters of a gas system is solved. A compact storage scheme is employed which makes the method commercially attractive.