The aim of this paper is to demonstrate how integrated resource planning (IRP) oriented to the gas sector can be applied both in new networks and in mature networks, and to present the advantages of its application. One case study is described, in the western central region of Portugal, to illustrate the results of a pilot project on natural gas IRP implementation in a new network in the European Union (EU). The city of Burg, Germany, with a mature gas network with district heating was also analysed in terms of IRP potential. The most important phases of the integrated resource plan definition and implementation (especially those oriented to the demand-side) are presented, namely, the definition of the most efficient technologies (including solar energy), fuel-switching possibilities, a detailed study of the impacts in the economy, environment and society, and the policy incentives necessary to motivate the gas utility companies to perform IRP. In the main case study, the suggested implementation plan would lead to a reduction of around 4.7% in natural gas consumption. Additionally, 13.3% of cost-effective fuel switching from other competing forms of energy to natural gas can be achieved. A proposed EU energy services directive on mandatory energy-efficiency activities for gas and electricity distribution utilities in the EU, will promote the large-scale implementation of the proposed approach in Europe. (C) 2003 Elsevier Ltd. All rights reserved.