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