Southwest Airlines appears to be one of the biggest winners of oil's slide.
Southwest gained more than 2 percent on Monday after Goldman Sachs upgraded the stock to "buy" from "neutral" and said it expects the company to outperform its peers.
Southwest has gained about 124 percent this year, making it the best S&P 500 performer year-to-date.
It's also one of two S&P 500 companies to see triple digit gains this year, thanks to strong travel demand and falling oil prices.
U.S. oil prices settled at their lowest lowest level since July 2009 on Monday. The plunge in oil has reduced airliner's fuel costs by about a third, according to Bob McAdoo, an analyst at Imperial Capital, but he doesn't expect those saving to trickle down to consumers.