Oil spills have made Nigeria\'s troubled Niger Delta one of the most polluted places on Earth, requiring $1 billion and 30 years to clean up, a U.N. report says. The Nigerian government commissioned a study by the U.N. Environment Program that looked at 200 locations and 75 miles of pipeline and more than 4,000 soil and water samples, the Los Angeles Times reported Friday. \"Pollution from over 50 years of oil operations in the region has penetrated further and deeper than many may have supposed,\" the report said. There were more than 7,000 oil spills from 1970 to 2000, the Nigerian government said. The report focused on the activities of Shell Petroleum Development Co., the major oil operator during the period, which still produces about 40 percent of Nigeria\'s oil in partnership with the Nigerian National Petroleum Corp. The company, part of the Royal Dutch Shell group, has said the oil spills were caused by theft and sabotage. \"We clean up all spills from our facilities, whatever the cause, and restore the land to its original state,\" Shell said in a statement after the report was released. But the U.N. report called control and maintenance of oil facilities in the region inadequate. \"The Shell Petroleum Development Company\'s own procedures have not been applied, creating public health and safety issues,\" it said.