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The measurement of formation dielectric constant is gaining acceptance as a means of determining water saturation in reservoirs where the presence of fresh water precludes standard resistivity-based interpretation. Texaco has been active in the development of dielectric logging techniques and instrumentation fgr the past ten years. The first part of this paper describes the basic concepts of dielectric constant measurement and the equipment used to obtain these measurements. In wells where formation water salinities are very low, the dielectric log can be used to obtain accurate water saturation (S,) calculations. Using measurements of dielectric constant and porosity, Sw values may be obtained directly from a modified mixing law equation. Also discussed is a means of empirically modifying this equation to account for the effect of salinity on the dielectric constant. This technique is employed when the dielectric log is used in lower resistivity formations. The Texaco 20-megahertz dielectric log was evaluated in six wells in Central Sumatra during May, 1982. These wells contained formation waters of very low salinity and therefore provided an excellent opportunity to evaluate the logs ability to differentiate oil and fresh water intervals. Examples from the Minas and Kasikan Fields are included in the paper to demonstrate the value of dielectric log interpretation in Indonesia.