Stark, James H. 1897. Stark's Guide-Book and History of Trinidad including Tobago, Granada, and St. Vincent; also a trip up the Orinoco and a description of the great Venezuelan Pitch Lake. Boston, James H. Stark, publisher; London, Sampson Low, Marston & Company. (This book has an excellent description of a trip up the Orinoco as far as en:Ciudad Bolívar and a detailed description of the Venezuelan en:Pitch Lake situated on the western side of the Gulf of Paria opposite.)
MacKee, E.D., Nordin, C.F. and D. Perez-Hernandez (1998). "The Waters and Sediments of the Rio Orinoco and its major Tributaries, Venezuela and Colombia." United States Geological Survey water-supply paper, ISSN 0083; 2326/A-B. Washington: United States Government Printing Office.
Weibezahn, F.H., Haymara, A. and M.W. Lewis (1990). The Orinoco River as an ecosystem. Caracas: Universidad Simon Bolivar.
Rawlins, C.B. (1999). The Orinoco River. New York: Franklin Watts.