American Airlines (AAL) - Get Report  became the first U.S. airline to figure out how to turn unit revenue positive in the fourth quarter and for the foreseeable future.

Too bad, American. Now investors seem to care more about profit margin at a time when fuel costs are rising slowly and labor costs are rising precipitously.

On Friday, the day American reported a 1.3% unit revenue gain, ahead of competitors and its first positive unit revenue in two years, its shares fell 2% to $46.95. The stock has risen 0.56% year to date.

In general, rising costs seem to account for investor concerns, along with a bit of fear -- perhaps unwarranted -- over potential capacity expansion.

While American costs are clearly rising, the pace of the increase will diminish during the coming year -- which is first on our list of the top five facts from Friday's fourth-quarter call.

1. Costs are on the rise. 

In the fourth quarter, American's mainline cost per available seat mile (CASM) excluding fuel and special items rose by an eye-popping 10.3%. For the full year 2016, mainline CASM rose 6.1%.

In the current quarter, consolidated CASM excluding fuel and items is expected to rise 9%, reflecting a 2% capacity decline -- meaning costs will be spread over fewer available seat miles -- and higher salaries for maintenance and fleet service workers.

But for the full year, CASM ex-fuel and items will rise 4%. Chief Financial Officer Derek Kerr pointed to a second-quarter increase between 4% and 6%, a third-quarter increase between 1% and 3% and a fourth-quarter increase between zero and 2%.

2. Everybody wants to close the margin gap with Delta -- Good Luck.

American reported a fourth-quarter pretax margin of 7.9% and a 2016 pretax margin of 12.5%, the second best in its history. First-quarter margin is expected to range between 3% and 5%.

For the current quarter, United (UAL) - Get Report has guided toward a margin between 0.5% and 2.5%, while Delta (DAL) - Get Report has guided toward 11% and 13%.

American CEO Doug Parker said American can catch Delta, while United President Scott Kirby has said United will surpass both American and Delta by 2020.

"I very much believe we are on a path to close the gap," said Kirby during the United earnings call. "I feel more confident today, the more I know, that we are going to do it."

3. Wall Street may have overreacted to a remark by Chief Marketing Officer Andrew Nocella.

American said full-year 2017 capacity will rise 1%, with domestic capacity flat and international capacity up about 4%, reflecting three new flights in Pacific markets added in 2016 and increased seating on the 777-200s.

But during the call, Nocella commented, "As we look at the balance of international vs. domestic it wouldn't shock me if we slightly toned down international and add a little bit to domestic this year, but that's not the current plan."

The remarks were interpreted by some analysts and investors to mean that American could add domestic capacity. This apparently contributed to Friday's share price decline. Wall Street hates new capacity.

We think Nocella might be thinking that going forward he should stick to the script.

4. While Latin America has the world's fastest unit revenue growth, it also has the lowest margins.

A 10.3% gain for passenger revenue per available seat mile (PRASM) in Latin America, where American is by far the largest U.S. carrier, enabled the carrier to lead peers in unit revenue gains.

"If you have a large operation in Latin America right now, while that's a source of the improvement year-over-year, it's also the lowest margin client in the world right now," Parker said.

"There will be certain pockets that we fly to that are producing lower margin and others just because the world economies vary," he noted.

American President Robert Isom said Brazil PRASM "led the way" with a 53% gain, but "it still remains negative on a year over two-year basis." Also, Isom said, Mexico, Central America and Venezuela (where U.S. carriers have made massive capacity cuts) were all positive for the quarter.

However, he said, "Our Caribbean performance continues to remain under pressure from low-cost carrier capacity additions throughout 2016."

5. During the three years from the start of 2014 to the end of 2016, American has bought back fully a third of all of its outstanding shares.

As of Dec. 31, 2016, American had 507 million shares outstanding, down from 756 shares at the December close of the merger with US Airways, Kerr said. That means American has bought back 249 million shares.

Kerr said American repurchased 228 million shares at an average price of $39.41. Shares closed Friday at $46.95. So American's stock-buying gain amounts to at least $1.7 billion.

United has bought back about 20% of its shares since 2014, investing more than $4 billion to buy about 80 million shares, CEO Andrew Levy said on its call.

This article is commentary by an independent contributor. At the time of publication, the author held no positions in the stocks mentioned.