Namibia is part of the Southern African Customs Union, Preferential Trade Area for Eastern and Southern Africa (PTA), the Common Market for Eastern and Southern Africa (COMESA), and the SADC Free Trade Protocol; no tariffs exist on most goods moving between members. It also has signed bilateral trade agreements with over 20 major trading nations around the world. Imports from outside the union are subject to a common tariff rate based on the Harmonized System of Import Classification; most imports need licenses. South Africa levies and collects most of the customs and excise duties for the other members and then pays each a share, based on an established formula. Namibia has double taxation agreements with South Africa, the United Kingdom, Sweden, and Germany (but not the United States) and is a member of the United Nations, the World Bank, the International Monetary Fund, and the World Trade Organization.