The present leak was discovered on 20 December 2011, and came
from a break in a flexible line about 360 meters out from the
vessel that sends oil to tankers. At that time it had probably
spewed for hours before being noticed. Pollution from spilled
oil stains Nigeria’s Niger Delta region, with crude oil lapping
against beaches and leaving a black ring around creeks in an
area about the size of Portugal. Possibly 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. PS of 28 December 2011: An
environmental group said yesterday that an oil slick had
approached Nigeria's coastline after the Shell spill last week -
although Shell insisted that its spill had been largely
dispersed. See http://www.physorg.com/news/2011-12-oil-nigerian-
coast-major-shell.html