Material and energy balances are included in oil shale retorting data-analysis in order to cross-check the data for accuracy. Only to the extent that the balances close well can be have confidence in related results. "Then one or more balances are substantially inaccurate, we must try to understand why. If one of the flow rates is incorrect or if one of the material stream concentrations is inaccurate, we can often discover the culprit simply by inspection of the balances, and we can estimate a correction with a calculator. When two or more things are inaccurate, the problem becomes much more difficult and cannot usually be solved by inspection. A more systematic approach is needed. This report describes an automated method for estimation of errors in five flow rates simultaneously, based on discrepancies in six balances. Since there are more equations than unknowns, the system is over-determined. The one remaining degree of freedom is used to statistically average out errors in material stream concentrations. This method has great advantages over trial and error or inspection methods because of its speed and convenience. In addition, the statistical procedure provide estimates of the significance of any corrections to errors in flow rate. This gives us an objective, quantitative criterion by which to decide whether a correction is warranted. The current formulation will not estimate corrections to any of the material stream compositions if they should be faulty. However, it will indicate when such faults exist through interpretation of significance of flow corrections. The formulation can easily be extended to correct errors in compositions, as well as errors in rates.