Reuters Market Eye - Jet Airways gains 3.7 percent,
Shares up 64.8 percent since Nov. 25, as of Monday's close.
Oil dives 4 percent to five-year low on oversupply worries.
Every $1/bbl fall in crude can boost company's FY16 oper profit estimate by 4-5 percent, say analysts.
Weakness at rivals will also boost sales, say traders.
SpiceJet cuts fleet size to save costs.
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(Reporting by Abhishek Vishnoi)