Richardson's visit, the first by a US energy secretary to Saudi Arabia in almost nine years, comes as the Saudis consider opening their energy sector to American oil companies. The move would provide a rare investment opportunity since the country's oil industry was nationalized in the 1970s.

No commercial deals for energy investments will be signed on Richardson's trip because the Saudis are still reviewing proposals submitted by US oil companies, according to government and industry sources.

Several American oil company executives, including those from Chevron Corp and Texaco Inc , recently made presentations to Saudi officials on possible energy deals.

"We are very encouraged by the results of our discussions over the past two days," Chevron chairman Ken Derr said in a statement after three days of talks in Riyadh.European-based Royal Dutch/Shell Group also dispatched a top official to meet with the Saudis. Richardson met with executives from several American oil firms wanting to do business in the region. He also plans to meet with Saudi Arabia's oil minister and other top officials.

Richardson, the former U.S. ambassador to the United Nations, has said he is making the trip to enhance the energy ties between the United States and Saudi Arabia. Saudi Arabia supplies the United States with 16 per cent of its crude imports.