Biological formation of calcium carbonate, catalyzed by purified urease enzyme or urease enzyme produced by a bacterium isolated from a Canadian oil field, were studied in batch systems. The extent of enzymatically produced CaCO3 increased with increases in enzyme and reactant concentrations, as well as temperature. In the presence of bacteria, the quantity of produced CaCO3 was dependant on urea concentration, with the highest amounts achieved with 15 g/L urea. The maximum concentration of CaCO3 produced enzymatically (57.6 g/L) was 2.6 times higher than that achieved in the presence of bacteria (21.5 g/L). Bacterial production of CaCO3 was less sensitive to temperature, whereas CaCO3 production rates with the urease enzyme were enhanced as temperature increased from 20 to 50degrees C. Plugging studies in unconsolidated porous media and in a core-flooding system with Berea sandstone indicated that in situ formations of CaCO3 could effectively reduce the permeability of porous media and can be used as an efficient approach in enhanced oil recovery operations.