The bacterial degradation of oil and fats comprises a combination of complex biological and physicochemical processes, such as the production of lipase, the lipolytic reaction, the mass transfer properties for the substrate phase, the fatty acid uptake and the growth kinetics of the cells. Microbial lipase production often depends on one or more of the following parameters: growth media composition (in particular the enzyme inducing compound), substrate concentration, growth rate, fermentation process design (i.e. batch, fed-batch or continuous operation mode) and interfacial area between lipid and water phase. The strain Geobacillus thermoleovorans IHI-91 is a member of a group of thermophilic bacteria, which show a high lipolytic activity. Kinetic studies with G. thermoleovorans IHI-91, growing aerobically on olive oil as the only carbon and energy source, show that oxidation of the liberated long-chain fatty acids rather than hydrolysis is the rate-limiting step.