Although prior research has highlighted that individuals differ in their ability to identify opportunities for entrepreneurial action, little attention has been paid to the effects that differences across opportunities may have on their initial identification. Integrating theoretical work on the nature of entrepreneurial opportunities with cognitive science research on the use of similarity comparisons in making creative mental leaps, we develop a model of opportunity identification that examines the independent effects of an opportunity idea's similarity characteristics, and the interaction of these characteristics with an individual's knowledge and motivation. We test this model with a within-subject experiment where we asked two samples of entrepreneurs to form beliefs about opportunity ideas for technology transfer. Results indicate that the superficial and structural similarities of technology-market combinations impact the formation of opportunity beliefs, and that individual differences in prior knowledge and entrepreneurial intent moderate these relationships. In addition to casting light on cognitive reasons why some entrepreneurial opportunities may be more or less difficult to identify, our theorizing and findings point towards reasoning strategies that may facilitate the identification of multiple (and potentially more valuable) opportunities, not only for new technologies, but also for new products, services, and/or business models.