In contractual relationships involving payments for environmental services, conservation buyers know less than landowners know about the costs of contractual compliance. Landowners in such circumstances use their private information as a source of market power to extract informational rents from conservation agents. Reducing informational rents is an important task for buyers of environmental services who wish to maximize the services obtained from their limited budgets. Reducing informational rents also mitigates concerns about the "additionality" of PES contracts because low-cost landowners are least likely to provide different levels of services in the absence of a contract. Paying low-cost landowners less thus makes resources available for contracts with higher opportunity cost landowners, who are more likely to provide substantially different levels of services in the absence of a contract. To reduce informational rents to landowners, conservation agents can take three approaches: (1) acquire information on observable landowner attributes that are correlated with compliance costs; (2) offer landowners a menu of screening contracts; and (3) allocate contracts through procurement auctions. Each approach differs in terms of its institutional, informational and technical complexity, as well as in its ability to reduce informational rents without distorting the level of environmental services provided. No single approach dominates in all environments. Current theory and empirical work provides practitioners with insights into the relative merits of each approach. However, more theoretical work and experimentation in the laboratory and the field are necessary before definitive conclusions about the superiority of one or more of these approaches can be drawn.