The pressure release bubble nucleation technique was used to study the kinetics of bubble nucleation for the H2O/CO2/Pyrex system over the supersaturation range 1-7. Attempts to fit the experimental bubble evolution data to the nucleation equation of Wilt (J. Colloid Interface Sci. 112, 530 (1986)) reveal apparent anomalies between the dependence of the predicted and that of experimental rates on supersaturation. These differences are explained in terms of a distribution of active nucleation sites at which the bubbles nucleate on the Pyrex surface. Each site type displays its own rate kinetics, and the overall bubble nucleation rate is the sum of the rates from each site type. The concept of "nucleation rate dispersion" is introduced to the field of bubble nucleation kinetics.