The Rangely Weber Sand Unit is a mature giant oil field that is currently under tertiary recovery with CO2 The Rangely oil field has been developed in stages, as have most large oil fields. This staged development over 50 years has had a significant impact on the distribution of remaining movable oil. Simulation studies indicated that oil cut could be improved if injection patterns were modified by shutting in injection wells to take advantage of relative well maturity. A field pilot project based on these studies has yielded results that indicate improved economic performance because of lower operating costs related to improved oil cut and reduced well maintenance.