In the midwestern United States, ethanol produced from corn is mixed with gasoline to meet clean air standards. Allocating land to produce clean fuel means taking away land from farming. We examine a model in which a scarce fossil fuel (e.g., oil) causes pollution but may be substituted by a clean fuel produced from land. Methodologically, we extend the Hotelling model to consider a substitute produced in the agricultural sector. We discover a range of prices within which the land-based fuel may substitute for the fossil fuel. When land is abundant, the supply of the clean fuel may exhibit multiple discontinuities. Environmental regulation may cause food production and farm prices to remain constant for a period of time.