This paper examines the determinants of aggregate flows of service trade in MENA countries using an adapted version of the gravity model and a panel dataset covering the 2000- 2009 period for 21 countries and 10 sectors. A new determinant of trade performance is introduced: the number of commitments undertaken by sector in the WTO as well as the availability of those commitments by mode. The results show that being a WTO member boosts trade in services. In addition, the number of commitments and binding these commitments increase exports, imports and trade in services. This positive and significant effect remains robust even after controlling for several econometric issues, namely the selection bias related to the WTO membership and the endogeneity of commitments.