Shares of Spirit Airlines gained 3 percent after Credit Suisse upgraded the company to "outperform."
The firm also increased its price target to $55 from $44, implying a 25 percent upside to the stock's Monday closing price of $43.85.
In Credit Suisse's note, the firm said it expects Spirit's earnings to grow by 15 percent in 2017 despite higher fuel costs, "which is unique among [its] coverage."
The firm also cited Spirit CEO Robert Fornaro's investment in operations will pay off.
"Improved operational performance should result in better load factors for [Spirit Airlines] over time and is a natural evolution of the model to improve the brand and take greater share from legacy carriers (the same way Ryanair has in the EU)," the firm said in its note.
Spirit Airlines shares are up 10 percent this year, but down 29 percent in the last 12 months.
Disclosure: Credit Suisse acts as a market maker in Spirit Airlines, which is also an investment banking client of the firm.