This paper presents a generalized procedure for optimizing steady-state operation of natural gas networks based on different objectives: minimum fuel consumption, minimum fuel cost, maximum throughput, and maximum operating margin (profit). The generalized procedure is a hierarchical approach that combines linear and non-linear optimizers in order to achieve good performance without compromising accuracy in modeling physical network components (compressors, pipes, etc.). The non-linear optimizer is used to optimize the physical flows in the transmission networks. The non-linear optimizer calls the linear optimizer to find the optimum allocation of flows among the contracts for the best objective function. The solution technique used by the linear optimizer can handle thousands of contracts with and without two-tier priced structure. Separating the physical flow optimization and economic optimization makes the global optimization feasible for large problems usually encountered in the gas transmission industry. In that sense, the present optimization method bridges the gap between engineering modeling and economic dispatch optimization of natural gas networks.