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2. American Gas Association, 1981, Gas facts, Arlington, Virginia, 211 p.
3. American Petroleum Institute, 1980, Reserves of crude oil, Natural gas liquids, and natural gas in the United States and Canada as of December 31, 1979. vol. 34, 253 p.
4. Geological Survey Bulletin;P. Averitt,1975
5. Bonatti, E., 1981, Metal deposits in the oceanic lithosphere,in C. Emiliani (Ed.) The sea, the oceanic lithosphere: John Wiley & Sons, New York, p. 639?686.