Abstract Least-squares techniques used to adjust experimental data, such as flow rates and concentrations (or size distributions, …) in a process flow-sheet, produce variables estimates which are consistent with respect to mass conservation laws. The sensitivity of this processing method is studied by calculation of the estimate variances. The method used consists of linearizing the mass balance equations and studying the effect of small disturbances created on the true values. The technique is applied to the generalized least-squares method as well as to the two-step least-squares method and in each case separate formulae are given for flow rates and concentrations. To illustrate the influence of various conditions on the mass balance results reliability, the equations are applied to a single node separator. It appears that very different amounts of information, with respect to the flow rates calculation, may be contained in stream concentrations. It is stated that the component which concentrates in the low flow rate product stream greatly contributes to flow rate value reliability. Application of this sensitivity analysis technique to a cement clinker grinding circuit, with its dedusting system, is used to demonstrate the usefulness of the method to evaluate mass balance reliability and to determine the experimental procedures and the data required to correctly balance industrial processes.