Software metrics have been studied in the procedural paradigm as a quantitative means of assessing the software development process as well as the quality of software products. Several studies have validated that various metrics are useful indicators of maintenance effort in the procedural paradigm. However, software metrics have rarely been studied in the object oriented paradigm. Very few metrics have been proposed to measure object oriented systems, and the proposed ones have not been validated. This research concentrates on several object oriented software metrics and the validation of these metrics with maintenance effort in two commercial systems. Statistical analyses of a prediction model incorporating ten metrics are performed. In addition, a more compact model with fewer metrics was sought, analyses performed, and also presented.