{HEAD ~ Oil} is extracted from {TAIL ~ the oil recovery zone} through an outlet opening at the intermediate level of the oil stratum in the zone 
is extracted from
{ HEAD ~ Oil } is extracted from { TAIL ~ the oil recovery zone } through an outlet opening at the intermediate level of the oil stratum in the zone
HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH