A method for estimating immobilized enzyme reaction progress curves, using simultaneous non-linear regression analysis of 2-3 substrate concentrations with time, is presented. These facile procedures involve using nested Gauss-Newton curve fitting algorithms on a Microsoft EXCEL spreadsheet. We refer to our technique as "nested" because the analysis consists of two or three mutually parameter-dependent sets of computations associated with bi- or termolecular enzyme-catalyzed reactions, respectively. We have applied the method to immobilized glucose oxidase-catalyzed reactions ([D-glucose] and [O-2] with time) and found that the kinetic parameters from initial velocity data were similar to those determined by the nested curve fitting method discussed herein.