Nigeria and Angola are facing increased competition for their crude exports, leading to the biggest slump in West African prices in 18 months. Rising supplies of shale oil from North Dakota and Texas via pipelines and railroads to the Gulf Coast, where almost 50 percent of US refining capacity is located, are sapping demand for costlier imports from Africa just as production in Libya recovers following the overthrow of Muammar Gaddafi. Libya will pump about 800,000 barrels a day by year-end, from 600,000 barrels now, Nuri Berruien, the chairman of state-run National Oil Corp. said in a Nov. 13 interview. “Libyan production is coming back,” said Roy Jordan, a London-based analyst at FACTS Global Energy who worked for more than 30 years at Royal Dutch Shell Plc, Europe's biggest oil company. “It's good-quality crude and that's been putting pressure on Nigerian grades. There is a growing availability of domestic crude in the US” too, he said. The premium of Nigeria's Qua Iboe crude to Dated Brent, a regional benchmark grade, narrowed more than 27 percent in October to $2.78 a barrel, the largest monthly decline since April 2010, according to data compiled by Bloomberg. It was at $1.88 today, the lowest in almost four months and down from a three-year high of $4.35 on Sept. 6. Dated Brent was at $111.98 a barrel, up 21 percent this year. Nigeria and Angola, Africa's biggest producers, are scheduled to ship the most oil since July this month. Combined exports will average 3.91 million barrels a day in November, according to loading programs obtained by Bloomberg. They have averaged 3.8 million barrels this year. Exports of the 12 biggest North Sea crude grades, of similar quality to Nigerian oil, will rise to 2.33 million barrels a day in November, the most since April, after planned work ended last month at the Buzzard field, loading data show. “It is still a tight market, but not as tight as it was,” said Torbjoern Kjus, an Oslo-based senior oil market analyst at DnB NOR, Norway's biggest bank. “One of the key reasons is the return of Libyan exports and higher production in the North Sea where field maintenance is over and Buzzard problems are smaller than they were.” Libya pumped 345,000 barrels a day in October, more than triple the 100,000 barrels it produced in September, Bloomberg data show. The country supplied almost 1.6 million barrels a day in January, before the fighting to oust Qaddafi erupted.