Production and storage tankers are being evaluated extensively for development of marginal oil and gas fields in the North Sea. The main safety aspects of these vessels are discussed, based on a number of quantitative risk assessments for these vessel concepts. These studies have confirmed the importance of several important safety features, such as a fire-protected, enclosed escape way along one of the sides of the ship. Other important safety features include weather-vaning capability as a function of the turret location, location and configuration of the flare system, protection of cargo tanks by inert gas blanketing, as well as procedures for strict control of tank intervention. The results, show that the production and storage vessels have favorable safety characteristics, and that these concepts represent an acceptable and feasible solution for the marginal fields.