Electronic service quality, or e-service quality, is the quality experienced by the user of a service delivered over the Web. Over the past several years, researchers have developed many models of e-service quality with the goal of identifying those factors that are most important for customer loyalty. Most of these models focus primarily or exclusively on retail e-commerce Web sites which support the delivery of a physical product to the consumer. Recently, however, “pure” e-service Web sites, namely those that do not involve the sale and delivery of a physical good, have received increasing attention from researchers. This article proposes and validates a quality assessment instrument for a type of pure e-service that has not yet been studied: a Web-based decision support system. Based on a study involving over six hundred subjects, we identify those quality dimensions that affect customer loyalty for a pure e-service of this type.