This article in the Economist (subscription required) reports on three different analyses of GATT and its successor, the World Trade Organization, and what their effects may have been on world trade, necessarily a counterfactual analysis. As Austrians might expect, the upshot of the three taken together is . . . not as much as many think, nor as good.
Since the article is “premium content” (you have to $ub$cribe to Economist.com), I’ve tried hereand here and here to provide links to the analyses directly.