Higher passenger traffic but lower average revenue per mile has Southwest Airlines Co. cruising at about the same altitude as last year.

Southwest is scheduled to release second-quarter financial results before the stock market opens Thursday. The Dallas-based airline is expected to show slight increases in profit and revenue compared with the same period of 2012.

WHAT TO WATCH FOR: The second quarter covers the early part of the summer vacation season, so it’s usually a good time of year for airlines. Investors will be interested in anything that Southwest says about travel demand, including whether there might be a chance to push fares higher.

Traffic has been healthy on Southwest and its AirTran Airways affiliate — it rose 2.6 percent in the quarter.

But revenue trends haven’t kept pace. A key statistic used to track revenue per mile declined between 4 percent and 5 percent in April, 2 percent in May and 1 percent in June compared with the same months in 2012.

That’s a sign of weak average prices. It could mean that Southwest isn’t selling as many seats at higher prices or it’s selling too many tickets at sale prices — or both.

WHY IT MATTERS: Southwest carries more passengers within the United States than any other airline and has an oversized influence on prices charged by rivals.

If Southwest thinks demand is strong, that could signal there’s room for fare increases, which would help boost revenue at other carriers too. But if Southwest is worried that higher prices will cause passengers to stay home, it could block other airlines from trying to raise their fares.

WHAT’S EXPECTED: On average, analysts surveyed by FactSet expect Southwest to report first-quarter earnings of 37 cents per share. That excludes special items such as paper gains or losses in Southwest’s fuel-hedging transactions. The analysts peg revenue at $4.66 billion.

LAST YEAR’S QUARTER: In the second quarter of 2012, the Dallas-based company reported net income of $228 million, or 30 cents per share. Excluding special items, the gain would have been 36 cents per share. Revenue was $4.62 billion.

Copyright (2013) Associated Press. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.