Acceptor doped perovskites such as strontium cerate form a variety of point defects through reaction with surrounding gases at high temperature, namely protons by dissolution of water vapour, electron holes by dissolution of oxygen and electrons by loss of oxygen. The defect equilibria can be described by three equilibrium constants coupled with electroneutrality and site conservation constraints. This work describes a numerical solution of these equations for arbitrary oxygen and water vapour partial pressures, without the need to neglect minority defects. It further examines the charge compensation mechanisms that dominate under the different regimes and their implications for transport properties.