Companies increasingly outsource IT-related tasks using reverse auction mechanisms embedded into online marketplaces. However, a considerable proportion of auctions at these marketplaces do not result in a contract between buyer and supplier. Extant literature mostly refers to costly bidding and bid evaluation to explain this phenomenon. Another possible explanation is that because of the low entry barriers, buyers with a low commitment to exchange can use the marketplace solely for information gath-ering purposes such as price benchmarking and obtaining free consultations, having little or no intention to contract a supplier. We test this explanation by looking at how different types of costs incurred by the buyer during the sourcing process, are related to the outcome of reverse auctions in terms of contract award. We argue that higher levels of search, preparation and negotiation costs are associated with higher commitment to exchange and find that opportunistic behaviour does indeed play a part in the non-contracted projects, while committed buyers are more likely to enter into a contract with a supplier. The hypotheses are tested on a sample of 2,574 reverse auctions at a leading online marketplace for IT services and further verified across projects of different value and different levels of buyer experience. On the practical side, we recommend setting up entry barriers for buyers with a low level of commitment.