LAGOS, Nigeria (AP) -- An oil spill near the coast of Nigeria is likely the worst to hit those waters in a decade, a government official said Thursday, as slicks from the Royal Dutch Shell PLC spill approached the southern shoreline.
The slick from Shell's Bonga field has affected 115 miles of ocean near Nigeria's coast, Peter Idabor, who leads the National Oil Spill Detection and Response Agency, told The Associated Press. Idabor said officials expect the slick to reach beaches in Rivers state by Thursday afternoon.
Shell, the major oil producer in Nigeria, said Wednesday the spill likely occurred as workers tried to offload oil onto a waiting tanker. The company published photographs of the spill, showing a telltale rainbow sheen in the ocean, but said it believes that about 50 percent of the leaked oil has already evaporated.
The source of the leak has been plugged, Idabor said, but the spill still threatens the shoreline and wildlife. Idabor said experts from Britain were coming to help with the cleanup.
Shell announced Wednesday that the Bonga spill likely was less than 40,000 barrels, or 1.68 million gallons. About the same amount of oil spilled offshore in 1998 at a Mobil field.
"Since the Mobil spill, this is just about the most major one," Idabor said.
Bonga sits about 75 miles (120 kilometers) off Nigeria's coast. It can produce about 200,000 barrels of oil and 150 million cubic feet of gas a day, according to Shell's Nigerian subsidiary. Production at the field has been halted since the discovery of the spill.
Environmentalists blame Shell for polluting the country's oil-rich Niger Delta. Some environmentalists say as much as 550 million gallons of oil poured into the delta during Shell's roughly 50 years of production in Nigeria -- a rate roughly comparable to one Exxon Valdez disaster per year. An estimated 11 million gallons was released during the 1989 Exxon Valdez spill in Alaska.
Shell in recent years has said most of the spills in the delta are caused by thieves tapping into pipelines to steal crude oil, which ends up sold into the black market or cooked into a crude diesel or kerosene.
Slicks from the Bonga spill likely will reach beaches near Forcados on Thursday, affecting wildlife there, Idabor said.
Nigeria, an OPEC member nation producing about 2.4 million barrels of crude oil a day, is a top supplier to the U.S.
Royal Dutch Shell PLC: http://www.shell.com