Slippage rates for corn and wheat are estimated using a simultaneous system explaining per-acre yields, input usage, technical change, and levels of participation in government programs. Soybeans are included due to cross-compliance requirements and because they substitute for corn in production. Slippage rates for wheat are in the range of 29-37% and for corn in the range of 48-58%. The results imply that efficient design of commodity programs must account for the slippage of aggregate yields due to changes in land quality and the use of constrained resources over fewer acres.