Michele L. W. Tuttle, Ronald R. Charpentier, and Michael E. Brownfield,1999 ,The Niger Delta Petroleum System: Niger Delta Province, Nigeria, Cameroon, and Equatorial Guinea, Africa: U.S. Geological Survey Open-File Report 99-50-H < http://pubs.usgs.gov/of/1999/ofr-99-0050/OF99-50H/ChapterA.html >
Michele L. W. Tuttle, Ronald R. Charpentier, and Michael E. Brownfield,1999 ,The Niger Delta Petroleum System: Niger Delta Province, Nigeria, Cameroon, and Equatorial Guinea, Africa: U.S. Geological Survey Open-File Report 99-50-H < http://pubs.usgs.gov/of/1999/ofr-99-0050/OF99-50H/ChapterA.html >