A method is presented for quantifying the uncertainty in two- and three-component tracer-based hydrograph separations. The method relates the uncertainty in computed mixing fractions to both the tracer concentrations used to perform the hydrograph separation and the uncertainties in those concentrations. A two-component example and a three-component example illustrate the application of the method. The three-component example yields uncertainty results very similar to those from a previously published Monte Carlo analysis and requires less computation. ¿ 1998 American Geophysical Union