Injection of water, steam, gases or chemicals into underground reservoirs to cause oil to flow toward producing wells, permitting more recovery than would have been possible from natural pressure or pumping alone.
Removal of some of the heavy oil left in an oil well after primary and secondary recovery. See primary oil recovery, secondary oil recovery.
Secondary and tertiary techniques for recovering crude from a pool. Oil is recovered other than by the natural pressure in a reservoir. These methods increase the proportion of oil recovered, but at additional cost.