This thesis presents different optimization models for the natural gas value chain. It focuses on the new challenges faced by the participants in the value chain for Norwegian gas after the liberalization of the European gas markets. Most of the models have a producer perspective and are designed to help analyze the value chain for natural gas and give decision support for the gas producers. The modelling framework in this thesis consists of linear programming, mixed integer programming, quadratic programming, stochastic programming and mixed complementarity problems. The thesis consists of this introductionary summary and four papers. Some of the work in this thesis has been sponsored by the VENOGA and the RAMONA project. VENOGA is a project involving Statoil, the Research Council of Norway, NTNU and SINTEF. The goal of the project is to build decision support models and competence for efficient operation and coordination in value chains where Norwegian gas is central. The RAMONA project involves the University in Stavanger, the University in Bergen, NTNU, SINTEF, Statoil, Gassco and CognIT. The intention with the project is to develop methods to optimize regularity and security of supply for the Norwegian gas production- and transportation system.