Pricing rules for PES auctions: Evidence from a natural experiment

Payments for Ecosystem Service (PES) schemes increasingly use auctions to target funds to low-cost providers, aiming to increase value-for-money. To date, PES auctions have most often employed “Pay-as-Bid” (PaB) pricing, in which successful participants are paid the amount stipulated in their bid(s). Alternative pricing rules exist, such as the “Uniform Price” (UP) rule, in which successful bids receive the same per unit payment determined by the marginal bid. Despite being successfully applied in other settings, the use of UP pricing in PES auctions has been limited. We explore the impact of UP pricing in the context of a scheme incentivising farmers to reduce nutrient run-off. Following our intervention, the auction through which contracts were allocated to farmers switched from PaB to UP. Our analysis provides the first real-world, causal evidence on the effect of alternative auction pricing rules in this context. We find that UP pricing reduced mean bids, by 40%. A priori the impact on payments made to the farmers is ambiguous, yet we find these to be reduced by a similar amount. Moreover, the UP format reduces the incidence of costly bidding behaviours, updating and sniping, by approximately 50% and 30% respectively. These significant and substantial changes suggest wider adoption of UP pricing in PES auctions is likely warranted.