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Combinatorial procurement auctions enable suppliers to pass their potential cost synergies on to the procuring entity and may therefore lead to lower costs and enhance efficiency. However, bidders might find it profitable to inflate their stand-alone bids in order to favor their package bids. Using data from standard and combinatorial procurement auctions, we find that bids on individual contracts in simultaneous standard auctions without the option to submit package bids are significantly lower than the corresponding stand-alone bids in combinatorial auctions. Further, no significant difference in procurer’s cost as explained by auction format is found.