photo of oil pump-jacks
Pump-jacks nod among strips
of ripening wheat in the South Field.
J. Agee photo

The primary stage in petroleum recovery is the pumping of crude oil pools, which amount to about two percent of the total available resource. Secondary recovery uses water to float oil from surrounding sands. Tertiary recovery uses acid and explosives to "wring out the rocks." The South Field, on the Blackfeet Reservation, is in secondary recovery.

The Cut Bank Field, where these pumps work amid strips of grain, has reached the tertiary stage.