The objective of our research is the development of a system resembling a CO2 scrubber, in which carbonic anhydrase catalyzes the rate of CO2 hydration for subsequent fixation into stable mineral carbonates. The present focus is on the use of produced waters as one of various possible sources of the counterions for precipitation. Carbonate precipitation has been studied from synthetic brines corresponding to a range of compositions of produced waters from the Permian and San Juan Basins, and promising results have been obtained with carbonic anhydrase. CO2 sequestration capacities are estimated to be 0.49-1.85X10(3) tonnes CO2/year and 1.28-2.80 x 10(5) tonnes CO2/year for the San Juan and Permian Basins, respectively, per cycle, up to similar to 3mt CO2 per year total, based on the volumes of produced waters in 2002. (c) 2005 Published by Elsevier B.V.