Key assumptions of the model include identical production technologies in trading countries and limited mobility of selected inputs. By imposing identical technologies, the Heckscher-Ohlin model invokes the notion of absolute advantages, rather than comparative advantages, as opportunity costs are the same in trading countries. Despite this less rigorous formulation, which is somewhat consistent with the virtual water perspective, the empirical model performed poorly in predicting trade patterns among the 63 countries in the author’s analysis. They, too, find that observed trading patterns are independent of water resource endowments.