This is a monograph for geophysicists and geologists on methods of studying oil and gas strata by means of a combination of geological and geophysical techniques, based on concrete data from the fields of the North Caucasus. It deals with the geophysical and geological interpretation of well logs to study regional structure, and the application of well-log data to study of reservoirs and estimation of oil and gas potential. At the time of original publication in the Soviet Union, Professor Simon Itenberg, D.Sc., held the chair of geophysics at the Grozny Oil Institute. Following ten years of practical well-site experience, he has been researching into the problems of well-site geophysics for the past 27 years. From 1966 to 1969 Professor Itenberg worked in India as a U.N. expert in this field. He has over 60 publications to his name, including textbooks and monographs.