The appropriate equations governing proton incorporation into perovskite oxides with an emphasis on high-temperature proton conductors (HTPCs) are reviewed. The prototypical compound SrCe0.95Y0.05O3 - delta is considered in detail. The mathematical approach of Poulsen is applied and the defect concentrations are modeled with a C language routine. A cluster-defect model is not considered here. Defect concentrations are calculated as a function of water vapor pressure and oxygen partial pressure. The solutions are presented in the form of two- and three-dimensional graphs of defect concentrations versus water vapor and oxygen partial pressures. Their physical meanings are explained by pertinent proton incorporation equations. Effects of water vapor pressure and A/B ratio on the n-p transition point are simulated.