Kinetics in photocatalytic reactions typically follow some form of the Langmuir-Hinshelwood rate law, and the kinetic parameters have usually been estimated using the method of initial rates. This method has serious drawbacks, primarily related to the subjectivity in estimating initial rates from experimental data. These drawbacks are discussed and illustrated using literature data. A superior approach using all the experimental data is described and compared to the method of initial rates. This technique is based on the Box-Draper method of non-linear estimation, coupled with a variable metric algorithm employing an alternative method for calculation of the gradient, It is shown that this approach results in better and more objective parameter estimates in these kinetic models,