Analysis of respirometric graphs for system diagnosis has recently drawn much attention due to the nature of the test being a fast method with reliable oxygen uptake (Ou) data. In this study, a new graphical analysis procedure is proposed, using the oxygen uptake rate (OUR) vs. Ou respirogram because of its distinct characteristics that provides easy visual inspection. The OUR plot is typically divided into two respiration phases, and each one of these phases can be simulated by a previously derived analytical equation. Based on the 2-phase model, five characteristic parameters (CPs) were derived for the OUR respirogram. Mathematically the 5 CPs can be related to the system parameters (SPs), including the four Monod kinetic parameters and two operating conditions (initial substrate and biomass concentration). Sensitivity analyses were then conducted to assess the 5 CPs for the level of effect caused by system parameters (SPs). This study also conducted respirometric tests under batch operation to evaluate the applicability of the graphical analysis method. Based on the 5 CPs estimated from the OUR respirogram of the tests, it can be concluded that respirometric tests normally experience the problems associated with initial lag, non-uniform seeding, and inadequate mixing.