EOR technologies applied to a new understanding of Residual Oil Zones (ROZ) are unlocking billions of barrels of oil in the Permian Basin. In an interview in Midland, TX, Steve Melzer of Melzer Consulting said, “For the longest time, we’ve thought the Permian had 100 billion barrels of oil in place,” now combining the region’s unconventional shale and ROZ , the Permian Basin could hold “800 billion, perhaps 1 trillion, barrels of oil.” Melzer and Bob Trentham, Director of the Center for Energy and Economic Diversification at U.T. Permian Basin conducted research under two RPSEA projects funded by the U.S. DPE’s National Energy Technology Laboratory. Trentham’s more conservative estimate is that ROS’s contain 300 billion barrels of oil or triple the previous reserve estimates for the Permian Basin. ROZ’s are opening up new production zones in areas through for decades to be non-productive. ROZ’s require CO2 EOR to develop. Melzer refers to ROZ’s as “Mother Nature’s Waterfloods.” Operators in the Permian Basin are beginning to take notice of the ROZ potential and are using horizontal drilling and CO2 flooding to produce from the new reserves, which mostly underlie existing EOR reservoirs. Among companies active in ROZ development are Russell K. Hall & Associates, Occidental Petroleum and Kinder Morgan.