A typology of models that explain patterns of variation in farm endowments and farm practices and yields shows that insecurity in renting land, financing constraints, and the absence of insurance generate patterns of factor use quite different from the famous “inverse relationship” caused by labor supervision problems. One might expect to observe positive relationships between wealth and yields. Village-level data from western Sudan confirm that such positive relationships are not a theoretical curiosity. Wealthy farmers have higher levels of output per hectare because they use more labor per hectare. Insurance and financing constraints appear to be the crucial market failures.