8 December 2025Conservation auctions are designed to allocate payments for environmental services to voluntary farmers. The auctioneer may announce either the maximum number of contracts (target-constrained auction) or, more commonly, the total budget available (budget-constrained auction). Building on Coiffard et al. (2025), who compared these twoformats, we introduce a new double-constraint auction, where both constraints — set at the same levels as in the benchmarks — are simultaneously disclosed to participants. Using the same experimental methodology, we assess performance consistent with a generic policy objective: maximizing environmental benefits while minimizing expenditures. On average, the double-constraint auction outperforms both target- and budget-constrained formats.