A rational polynomial function, i.e., the ratio of two polynomials, is suggested as a general correlating equation for rheometric data. Using data from the literature, it is shown that the rational-polynomial model is capable of accurately representing the rheogram of virtually any time-independent fluid. The utility of the rational-polynomial model in hydraulic calculations is demonstrated using data for a variety of drilling fluids. It is shown that the pressure drop in circular pipes is more accurately predicted using the rational-polynomial model than with the standard fluid models used in the petroleum industry.