This paper presents a mathematical analysis that allows the rate of H-2 + O-2 recombination and related heat generation in single-compartment electrolysis cells to be calculated as a function of current density and temperature. The analysis employs electrochemical kinetics and gas evolution-enhanced mass transfer theory. Recent calorimetric results of others during the electrolysis of K2CO3 + H2O solutions in the low current density range from 0.5 to 4 mA cm(-2) are in good agreement with the theoretical predictions. The fraction of O-2 recombining with H-2 decreases significantly with increasing current density. As much as 27% of the O-2 recombines at 0.5 mA cm(-2), but only 4% at 100mAcm(-2). It is shown that the heat generated by H-2 + O-2 recombination comprises a significant fraction of cell input energy only at low current densities. At 0.5 mA cm(-2), heat due to H-2 + O-2 recombination is 120%, but it decreases proportionally to j(-15), with values of 18% at 4mAcm(-2), 0.8% at 40mAcm(-2) and only 0.03% at 400mAcm(-2). The analysis also predicts quantitatively the observed enhancement of recombination by O-2 gas sparging and its elimination by N-2 sparging. On the basis of their results at low current densities, a group of researchers recently concluded that H-2 + O-2 recombination is the source for the ’excess heat’ reported by other groups and attributed by some to ’cold fusion’. However, reported excess heat values, ranging from a low of 23% at 14mAcm(-2) to a high of 3700% at 6mAcm(-2), are much larger than can be explained by recombination. Whatever the explanation for the large amounts of excess heat reported by various groups, H-2 + O-2 recombination must be rejected as a tenable explanation.