Combinatorial auctions have been suggested as a mean to raise efficiency in multi-item negotiations with complementarities among goods as they can be found in procurement, energy markets, transportation, and the sale of spectrum auctions. Since 2008 the Combinatorial Clock Auction (CCA), a two-stage auction format has been used in many countries. [8] tested CCA in the lab and found out that the efficiency of CCA was relatively low, since bidders tended to submit too few bids. To reduce bidders’ complexity concerning evaluating lots of bundles, we simplified the bidding language without losing efficiency. Hereby, we used the knowledge of super-additivity and the fixed descending complementarity type of our value model. In lab experiments, we tested the two phases of the CCA auction, namely the Combinatorial Clock + (CC+) auction and a sealed bid version, with the simplification separately. Both formats yielded in higher efficiency and revenue than the CCA.