Antigua and Barbuda is a twin-island nation lying between the Caribbean Sea and the Atlantic Ocean. It consists of two major islands, Antigua and Barbuda, and a number of smaller islands. The islands are low-lying with some higher volcanic areas. The government system is a constitutional monarchy with a parliamentary system of government and a commonwealth realm. The chief of state is the queen of the United Kingdom, and the head of government is the prime minister of Antigua and Barbuda. Antigua and Barbuda has an open market economy in which the prices of goods and services are determined in a free price system. Antigua and Barbuda is a member of the Caribbean Community (CARICOM) and the Organization of Eastern Caribbean States (OECS).