The Obama administration has declared South Sudan's oil sector open for business for U.S. companies.
Secretary of State Hillary Rodham Clinton says American investment in the sector was authorized last week after a request from the world's newest recognized country. South Sudan gained its independent in July.
The license is valid even when good must be shipped through Sudan. The U.S. has penalized Sudan because it is considered a state sponsor of terrorism.
Clinton told a conference on South Sudan that the new country must avoid the "natural resource curse" that ends with a small elite hoarding all the wealth.
American assistance to South Sudan is focusing on agriculture and private investment. Britain is helping with health care. Norway is aiding the oil industry and transparency efforts.