said oil removal means comprises an oil outlet opening to said oil recovery zone at said {TAIL ~ intermediate level} of {HEAD ~ the latter zone} 
said oil removal means comprises an oil outlet opening to said oil recovery zone at said { TAIL ~ intermediate level } of { HEAD ~ the latter zone }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD