Two conventional 7-7/8''diameter (200 mm) natural stone surface set diamond bits were instrumented and used to drill shale in laboratory controlled tests at simulated downhole conditions. Each bit had a different type of hydraulic flow design. The Christensen, Inc. MD262, a soft to medium formation bit, is a radial flow type of design whereas the other Christensen, Inc. MD331, is a medium to medium-hard formation bit, with a forced flow or feeder-collector hydraulic design. Miniature pressure transducers were mounted at different locations on the bit crowns. While drilling under a wide range of simulated conditions, output from these transducers were recorded. From these data, an understanding of the magnitude and distribution of pressures at the bit face was obtained. An analysis of the data showed that a substantial amount of hydraulic energy is expended at or near the crowfoot or center of the bits. Also, an estimate of pump-off force (or hydraulic lift) as a function of pressure drop was obtained from the pressure distribution data.