A 2005 US Department of Energy study into enhanced oil recovery (EOR) potential in California identified a significant opportunity for additional recovery and a theoretical storage capacity in excess of 3.4 billion tonnes of CO2. Such capacity would potentially be available from multiple fields and several different operators. See for reference:
http://www.netl.doe.gov/publications/proceedings/05/RCSP/pdf/PhaseI-WESTCARB.pdf