Shares in Frontier Airlines Holdings, parent of Frontier Airlines, rose 9 percent on Friday after the discount carrier said its traffic in April rose, soothing fears about competition at its Denver hub.

Southwest Airlines, the No. 1 US carrier by market value, started flights from Denver earlier this year, raising fears that Frontier's results would be hurt.

But Frontier said on Thursday that in April its load factor rose 4.4 percentage points from a year earlier to 80.7 percent.

The airline also said that revenue per available seat mile increased 6.8 percent to 8.27 cents.

The results were impressive given Southwest's presence in the market, said Helane Becker, an analyst at The Benchmark Co.

"Everybody has been very concerned about Southwest bringing fares down and putting pressure on Frontier," Becker said. "Putting it all together, we think it was a pretty good result for them."