A landmark UN report on oil pollution in Nigeria will be released on Thursday having already drawn controversy over blame for major spills in the native region of the late activist Ken Saro-Wiwa. The study of the effects of pollution in Ogoniland, part of the Niger Delta, the country\'s main oil-producing region, follows a two-year assessment by the United Nations Environment Programme. It is to be presented to President Goodluck Jonathan at 2:00 pm (1300 GMT) and to the media two hours later in Africa\'s largest oil producer. Ogoniland was the native region of Saro-Wiwa, the renowned environmental activist who was executed by the then-military government in 1995 after what was widely considered a show trial, drawing global condemnation. His activism and execution drew the world\'s attention to Ogoniland. Anglo-Dutch oil giant Shell, Nigeria\'s oldest and historically its largest operator, was forced to leave Ogoniland in 1993 following community unrest sparked by poverty and allegations of environmental neglect. ctivists say pollution has devastated Ogoniland, a community of mainly farmers and fishermen, and the UN report will mark the first major attempt to scientifically document the effects. \"We very, very much hope that this report will change the situation,\" said Audrey Gaughran of Amnesty International. \"For change to happen, the government of Nigeria must do much more and the companies have to stop blaming everybody else.\" Amnesty International has estimated that, if all types of oil pollution in the vast Niger Delta are added up over the past half-century, it would be \"on par with the Exxon Valdez every year over the last 50 years.\" The report has already attracted controversy and there were lingering suspicions ahead of its release. A UNEP project leader caused an outcry last year when he said an estimated 90 percent of oil spills in Ogoniland were the result of criminal activity rather than leakage from operations by a joint venture including Shell. Shell has said most oil spills in the delta are caused by sabotage and theft, an assertion strongly disputed by activists. UNEP has since said the study will not apportion blame and instead aims to map the location, nature, extent and implications of oil contamination. The survey was financed by the Shell-Nigeria joint venture under a \"polluter pays\" principle, but was peer reviewed by external scientists, UNEP has said. \"We have our fears and concerns about the outcome of the study. Shell might be the beneficiary because the study was co-financed by them,\" Movement for the Survival of Ogoni People spokesman Bariara Kpalap told AFP. Meanwhile, Oil giant Royal Dutch Shell on Wednesday accepted responsibility for two devastating oil spills in the Niger Delta which lawyers say have destroyed the livelihoods of a fishing community. The Bodo community took legal action in Britain against the Anglo-Dutch group over the spills in 2008 and 2009, which affected rivers and waterways over a large area. A spokesman for Shell\'s Nigerian operations, the Shell Petroleum Development Company (SPDC), said it would pay compensation but said the process could take several months.