In recent years, several countries have deregulated passenger railway markets to allow open access. The aim is for competition to lower fares and increase quality of service, thereby increasing demand, economic efficiency and overall social welfare. In this paper, we use a stylised simulation model to study how open access competition affects fares, demand, supply, consumer surplus and operator profits compared to a profit-maximising monopoly and to a welfare-maximising benchmark situation. We conclude that aggregate social welfare increases substantially when going from profit-maximising monopoly to duopoly competition, as consumers make large gains while operators’ profits fall.