The U.S. Bureau of Mines has maintained a continuing study of high- frequency acoustic emissions (ultrasonics), 30 to 150 khz, in relation to coal mine bumps and outbursts for several years. As part of the research effort to evaluate the nature of possible precursors based on high-frequency acoustic emissions, raw data signals that occur during mining were recorded and analyzed. A total of 753 ae (acoustic emission) events were obtained during three different recording periods in 1991 in a coal mine in eastern Kentucky. Seven different categories based on signal waveform characteristics were observed. Frequency analysis was conducted on several events from each category. This paper presents the results of the analysis and concludes that (1) higher frequencies than previously reported, up to 350 khz, are present in these signals, (2) the rate of high-frequency acoustic emissions may be used to study the stress transfer process in a coal mine, (3) seven different categories of ultrasonic signals were identified and described, and (4) continuous emission signals appear to be present that may be critical in studying precursors to ground failure in coal mines.