Experimental techniques have been developed to quantitatively evaluate in-situ H2S generation as a function of solution alkalinity, SO42− concentration, and carrier gas during thermal recovery processes. Experimentally, well-designed laboratory tests have been conducted to quantify the in-situ generation of H2S in a surface passivation reactor. The reaction gases were analyzed by using a gas analyzer, while the pH values were measured by using a glass electrode after adding anions or cations into the solution. Solution alkalinity is found to restrain the formation of H2S after subtracting the amount of H2S that neutralizes alkali in the solution. H2S production increases with increasing SO42− concentrations, more evidently at a high temperature. As temperature increases, using either carbon dioxide or nitrogen as carrier gas increases the H2S production; carbon dioxide as a carrier gas, however, yields more H2S up to 57.6% than nitrogen at temperature of 200-280°C. It is suggested that effect of pH of the formation water be taken into account while predicting the produced acid gas rates.