A theory describing bulk better operation is presented. The theory is applicable to a diatomic gas which adsorbs dissociatively on a getter material which exhibits a time independent sticking coefficient. The theory includes the effects of surface reactions and bulk diffusion. Exact numerical solutions are presented for the particular cases of pumping and desorption. In addition, approximate analytical solutions are derived and used to illustrate the characteristics of the particular operational regimes. The theory is applied to the analysis of the pumping and desorption behavior of the Zr‐Al alloy bulk getter. The predictions of the theory are in excellent agreement with the experimentally measured Zr‐Al performance.