"In situ processing of oil shale offers many environmental advantages. For example, the waste products largely remain underground and are not released into the immediate environment. There are also many technical problems connected with in situ processing, one of them being the gathering of information about the contents and the state of the oil shale retorts. A promising method for obtaining such information is electromagnetic remote sensing. In this approach, transmitters and receivers are introduced to the vicinity of the retort via boreholes (figure 1), and one attempts to extract information about the contents of the retort by analyzing the received signals. For this purpose, it is necessary to have a specific model which relates the relevant physical quantities and allows the interpretation of the signals."