Field tests were conducted to demonstrate the performance of an advanced development model borehole directional radar probe in coal measure rocks. Preliminary test site evaluations at five candidate coal mines were performed to determine the electromagnetic propagation parameters of the coal seams and to inspect available geologic mine hazards such as paleochannel sand cutouts, faults, and weak roof conditions as potential radar test targets. The York Canyon Mine near Raton, New Mexico, was selected as the demonstration site. Surface-operated tests in vertical boreholes as well as in-mine tests in horizontal boreholes were conducted using the radar probe, resulting in the detection of a near-vertical seam displacing fault. Other electromagnetic tests using separate source and receiving probes in vertical boreholes as well as in through-transmission tests in underground coal pillars provided useful data on the electromagnetic parameters of the coal and large-scale geologic structures.