AbstractAllocatable fixed inputs, such as land, are a potentially important source of jointness in agriculture. As with other causes of jointness, they necessitate multiple‐product systems for modeling product supply and input demand. In other important ways, however, their analytical implications are very different from other causes of jointness. Model specification differs. Demand functions for the quantities of each input used in the production of individual commodities can be derived if a primal approach is used, but such allocation equations cannot in general be identified from a dual specification. Available allocation data are not even useful in such dual estimations.