Currently, three strong ion models exist for the determination of plasma pH. Mathematically, they vary in their treatment of weak acids and this study was designed to determine if any significant differences exist in the simulated performance of these models. The models were subjected to a 'metabolic' stress either in the form of variable strong ion difference / fixed weak acid effect, or vice versa, and compared over the range 25 PCO₂ 135mmHg. The predictive equations for each model were iteratively solved for pH at each PCO₂ step and the results plotted as a series of log(PCO₂) / pH titration curves. The results were analysed for linearity using ordinary least squares regression and for collinearity using correlation. In every case, the results revealed a linear relationship between log(PCO₂) and pH over the range 6.8 pH 7.8, and no significant difference between the curve predictions under 'metabolic' stress. The curves were statistically collinear. Ultimately, their clinical utility will be determined both by acceptance of the strong ion framework for describing acid-base physiology and by the ease of measurement of the independent model parameters.