The first factor that differentiates cost studies is the type of model that is used to estimate the opportunity costs of land. There are three basic types of model. Bottom-up or engineering models generally use re- ported land prices to estimate the social cost of con- verting land from one use or practice to another (Dudek and LeBlanc 1990; Moulton and Richards 1990; New York State Energy Office 1991; Richards and others 1993; Richards 1997a; Sedjo and Solomon 1989; van Kooten and others 1992). These models are gener- ally limited in scope to the immediate on-site effects of a program or practice. Sectoral models estimate the opportunity cost of land based on supply and demand equations for the agriculture or forestry sectors (Adams and others 1993, Adams and others 1999; Alig and others 1998; Sohngen and Mendelsohn 2001; Sedjo and others 2001). The costs of various programs and practices are derived from estimates of changes in consumer and producer