American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. Abstract The objectives of well logging, logging operation and log analysis in the geothermal industry are considerably different from those in the petroleum industry. This paper discusses these differences. Usually the commercial logging companies provide well logging services using essentially the same equipments and procedure used in the petroleum industry. This creates some problems in quality assessment, normalization and calibration of logs. This paper discusses those problems with examples from geothermal wells in the Imperial Valley, California; Raft River, Idaho; and Jemez Mountains, New Mexico. Interpretation techniques of well logs used in the geothermal industry are borrowed in toto from the petroleum industry. Because of the inherent differences in the nature of petroleum and geothermal reservoirs, log interpretation techniques now used for geothermal wells often provide inaccurate or erroneous answers. This paper points out many such problems in interpretation and suggests improved procedure, where possible. Introduction Well logging operation and log analysis in geothermal wells are considerably different from those in the petroleum industry. These differences can be grouped under three main areas: logging objective, logging operation and log interpretation. In this paper we discuss these differences. Although the development of hardware and interpretation techniques for geothermal wells have begun in earnest, it will be many years before the new hardware and techniques become practical and standardized. At present, practically all the hardware and techniques in the geothermal well logging industry are borrowed in toto from the petroleum industry. This leads to many problems in logging operation, assessment of log quality and log interpretation in the geothermal industry. The purpose of this paper is to point out these problems and suggest remedies, where possible.