The economy of the Caribbean region is based mainly in the exploitation of natural resources such coal and natural gas, salt, agricultural products. Based on per capita income, the islands of the Caribbean are classified as middle-income countries except for Guyana and Haiti, which are classified as low-income countries. Mexico and the Dominican Republic have significant income bracket disparity with both low-income and high-income populations in the Dominican Republic. The individual economies of the Caribbean islands are generally open to free trade. The Caribbean's tourism-driven economy is thriving. The rise of tourism has sparked an indirect growth in many other domestic industries such as construction and many other service- and tourism-related enterprises. Offshore banking is also an important part of Caribbean commerce, particularly in The Bahamas and Aruba. St. Croix has one of the world's largest petroleum refinery facilities, as does Aruba. Mostly all of these industries, however, rank below tourism in profitability. Because most of the Caribbean's import-export business is with the United States and the majority of Caribbean tourists are U.S. citizens, the influence the U.S. economy has on the islands, economy is significant.