Alaska Airlines ( ALK) posted frosty first-quarter results on Friday morning, missing Wall Street expectations because of a sizable jump in fuel costs.

Alaska Air announced a first-quarter net loss of $42.7 million, or $1.59 a share, an improvement over the net loss of $56.3 million, or $2.12 a share, it had a year ago. Excluding a $2.4 million charge, the carrier would have lost $1.53 a share, still short of Wall Street's estimate of a loss of $1.35 a share, according to Thomson Financial.

Revenue came in at $598.4 million, up 16.4% from last year's $518.7 million, but a fuel-related jump in operating expenses helped eat into the carrier's top line-growth. Total expenses came in at $656.5 million, a 10.1% increase from the year-ago $596.5 million, driven by a 20.1% increase in fuel costs.

"The first quarter is traditionally our weakest, and this one included the added burden of high fuel prices and a severe winter storm," said Bill Ayer, chairman and CEO. "Despite these obstacles, we narrowed our year-over-year loss by $13.6 million, or 24.2%. But the bottom line is that we had a sizable loss, illustrating that we still have work ahead of us."

That said, Alaska Air's expansion plans appear to be working. In the first quarter, the carrier boosted capacity, measured in available seat miles, by 10%, while traffic, which is measured in revenue passenger miles, rose 13.9%.

And not only has demand outstripped supply, the company didn't necessarily have to slash ticket prices to do it. Unlike rivals, the company's yield, a measure of how much money it takes in per passenger, actually rose 1.9% in the first quarter.