I think they mean after a secondary recovery method like water flood.
From the DOE:
http://www.fe.doe.gov/programs/oilgas/eor/
Crude oil development and production in U.S. oil reservoirs can include up to three distinct phases: primary, secondary, and tertiary (or enhanced) recovery. During primary recovery, the natural pressure of the reservoir or gravity drive oil into the wellbore, combined with artificial lift techniques (such as pumps) which bring the oil to the surface. But only about 10 percent of a reservoir’s original oil in place is typically produced during primary recovery. Secondary recovery techniques extend a field’s productive life generally by injecting water or gas to displace oil and drive it to a production wellbore, resulting in the recovery of 20 to 40 percent of the original oil in place.
Yes, what I think I said. 35% recovery is pretty good and it goes down from there. Lots of fields have had pressure maintenance or water flooding for decades. Some though, like areas of the East Texas Field that have never been unitized into very big blocks have had either no or very spotty and ineffective water floods.
Primary recovery really depends on the driving mechanism of the reservoir. modes of primary recovery involve depletion (low recovery), water drive (higher recovery), compaction drive (higher yet recovery in primary mode).
Recovery in cases where the gas cap is destroyed early and the oil becomes immobile and unrecoverable is usually dismal and lots of oil was wasted and for all practical purposes lost forever.