This paper uses a gravity-like structure derived from a monopolistic competition model to measure market access among Canada, USA, Japan and EU Quad countries over the 1996-2001 period. We explore the overall asymmetry and 18 food industrial-level asymmetries of bilateral trade openness. Using actual bilateral estimates of tariffs and nontariff barriers, we investigate their role in explaining the trade reduction effect of national borders. A representative estimate of market access shows that higher asymmetries exist in USA, Canada and EU trade with Japan. Quite surprisingly, the last country is always more open than the reverse. Finally, we found that tariffs and NTBs explain a significant part of the border effects and that the NTB role is often higher than that of tariff.