Optimization of oil and gas field production systems poses a great challenge to field development due to complex and multiple interactions between various operational design parameters. Conventional analytical methods are capable of finding local optima. They are less applicable for efficiently generating alternative design scenarios in a multi-objective context. This paper presents an integrated workflow using a simulator coupled to an optimization framework. It is used to investigate the impact of design parameters while considering the physics of the reservoir, wells, and surface facilities. Experimental design methods are used to investigate parameter sensitivities and interactions. Optimization methods are used to find optimal design parameter combinations which improve key performance indicators of the production network system. The proposed approach is applied to a representative gas production system and is shown to be capable of finding optimal combinations of pipe sizes and compressor power. The method offers a significant advantage over existing conventional techniques.