Commercial distillation column simulators have become essential tools for engineers who design, troubleshoot, and evaluate distillation units. One area that needs to be improved is the procedure for fitting field data to a simulation model, which is essential in evaluating the mass transfer efficiency of existing units. The impact of the matching criterion, the methodology whereby computer-calculated values are compared against field-measured values during a trial and error procedure, on the perceived efficiency of a distillation column is demonstrated by two industrial cases. It has been shown that the commonly applied matching criteria often give questionable and inaccurate results. A new matching criterion is therefore developed to assist with the task. In this method, the objective function to be minimized in the data fitting is the sum of errors regarding the perceived efficiencies at the top, middle, and bottom locations. The calculation of the objective function can be programmed and incorporated into simulation software packages. For example, Pro-II offers CALCULATOR FUNCTION with the FORTRAN programming language. This gives an additional advantage of saving large amounts of time, especially when multicomponent data fitting is involved.