reacting the oxidant and fuel in {TAIL ~ the oxidizers} to produce heat to heat {HEAD ~ a portion} of the formation; and 
reacting the oxidant and fuel in { TAIL ~ the oxidizers } to produce heat to heat { HEAD ~ a portion } of the formation ; and
OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH