1. “A Primer of Oil-Well Drilling”;Baker,1979
2. American Petroleum Institute (1983), “1982 Joint Association Survey on Drilling Costs” Washington D.C., U.S.A.
3. “An Evaluation of Direct Use Project Drilling Costs”;Dolenc,1983
4. “Evolution du Cout des Forages Geothermique en France”;Champion,1983
5. “International Comparison of Low Enthalpy Geothermal Well Costs”;Mortimer,1984