Liberia is eligible for preferential trade benefits under the African Growth and Opportunity Act. The country's revenues come primarily from rubber and iron ore exports, and revenues from its maritime registry program. Liberia’s U.S.-owned and -operated shipping and corporate registry is the world’s second-largest. U.S. exports to Liberia include agricultural products (with rice as the leading category), vehicles, machinery, optic and medical instruments, and textiles. The main imports from Liberia to the U.S. are rubber and allied products; other imports include wood, art and antiques, palm oil, and diamonds. The U.S. and Liberia have signed a trade and investment framework agreement.