ABSTRACT It is well understood and documented that bottom-hole hydraulics plays an important role in conventional diamond bit performance. Recent industry experience has shown a similar importance with the new synthetic diamond compact bits. Certain types of polycrystalline diamond compact bits have cutters arranged in a reverse spiral mode. For optimum performance bit hydraulic design should be tailored to that reverse spiral mode. Theory reveals that a bit built with rectangular nozzles with a long axis in the tangential direction can give a fluid velocity envelope similar to the envelope of the reverse spiral. A rectangle can also reduce bit plugging by providing an increased perimeter in a non-concentric geometry. The introduction of rectangular nozzles into the bit renders the regular round nozzle pressure drop equation unsuitable for direct application. Extensive hydraulic tests were performed with different configurations of rectangular nozzles to establish more accurate pressure loss equations. The experiments included single nozzle studies and laboratory and field tests of bits. Field test results confirmed the reliability of the results obtained in the laboratory studies.