LONDON, May 31 (Reuters) – Downward pressure intensified on Nigerian oil, even as benchmark crude prices also tumbled by more than 3 percent, as an excess of light sweet crude built in the Atlantic basin. Angolan trading also slowed on the back of faltering Asin demand, but open arbitrage to the United States for medium and heavy crudes underpinned prices.

Source: http://feeds.reuters.com/~r/reuters/AfricaNigeriaNews/~3/hfUirQPTVHY/idAFL8N1IX5O7