The financial surplus of agriculture has been central to theories of the role of agriculture in economic development. Morrisson and Thorbecke (MT) have used a constant-price social accounting matrix (SAM) framework to rigorously measure the financial surplus of agriculture and decompose the mechanisms of surplus extraction. History and theory have, however, stressed the role of prices as an invisible transfer mechanism in addition to the visible transfers identified in the SAM framework. We extend the MT approach by defining and measuring the real surplus of agriculture and decomposing the mechanisms of surplus extraction between visible and invisible financial transfers. Using an archetype computable general equilibrium model for poor African nations, we trace the generation, transfer, and use of an agricultural surplus created by a productivity gain in agriculture. This shows that prices indeed play an overwhelmingly important role in transferring a surplus from agriculture to the benefit of the rest of the economy.