Claim: General Agreement on Trade in Services  is a treaty  created to extend the multilateral trading system to service sector and all of the WTO All members of the WTO are parties to the GATS.
Evidence: The treaty was created to extend the multilateral trading system to service sector, in the same way the General Agreement on Tariffs and Trade (GATT) provides such a system for merchandise trade. All members of the WTO are parties to the GATS.