Techniques based on 02 measurements such as gassing out or oxygen balance techniques which are generally used in determining K(L)alpha values are hardly applicable when a solid phase is present in the medium or during a fermentation process. In this study a new technique was used in achieving K(L)alpha values. This technique is based on the continuous response measurement of the outlet gas phase to a CO2 step change in the inlet. This method was applied to determine K(L)alpha values in a bubble column where a microbiological coal desulfurization process takes place using Thiobacillus ferrooxidans. To check the results obtained by using the CO2 mass balance technique, a series of runs were carried out to find the K(L)alpha value in an air/water system. The results were compared with previous ones already reported by other authors, and they were seen to be in good agreement. Other K(L)alpha values were achieved by using an inorganic salt solution as a growth medium for the bacterium and also as a liquid medium in the desulfurization experiments. It was found that K(L)alpha increased as the salt concentration increased. When a solid phase was introduced into the reactor K(L)alpha decreased as the amount of the solid present increased; however, K(L)alpha increased when the superficial gas velocity increased. Finally, other K(L)alpha values were obtained during various coal desulfurization runs. It was found that K(L)alpha remained constant throughout the reaction time, because T. ferrooxidans does not produce any substances that can alter the medium viscosity. It was also found that this method of determining K(L)alpha can be used during bacterial treatment without interfering with the microorganism action.