Firms' incentives to manufacture biased user reviews impede review usefulness. We examine the differences in reviews for a given hotel between two sites: Expedia.com (only a customer can post a review) and TripAdvisor.com (anyone can post). We argue that the net gains from promotional reviewing are highest for independent hotels with single-unit owners and lowest for branded chain hotels with multiunit owners. We demonstrate that the hotel neighbors of hotels with a high incentive to fake have more negative reviews on TripAdvisor relative to Expedia; hotels with a high incentive to fake have more positive reviews on TripAdvisor relative to Expedia. (JEL L15, L83, M31)User-generated online reviews have become an important resource for consumers making purchase decisions; an extensive and growing literature documents the influence of online user reviews on the quantity and price of transactions. 1 In theory, online reviews should create producer and consumer surplus by improving the ability of consumers to evaluate unobservable product quality. However, one important impediment to the usefulness of reviews in revealing product quality is the possible existence of fake or "promotional" online reviews. Specifically, reviewers with a material interest in consumers' purchase decisions may post reviews that are designed to influence consumers and to resemble the reviews of disinterested consumers. While there is a substantial economic literature on persuasion and advertising (reviewed below), the specific context of advertising disguised as user reviews has not been extensively studied.The presence of undetectable (or difficult to detect) fake reviews may have at least two deleterious effects on consumer and producer surplus. First, consumers who 1 Much of the earliest work focused on the effect of eBay reputation feedback scores on prices and quantity sold; for example, Resnick and Zeckhauser (