Southwest Airlines today reports what almost certainly will be its 69th-consecutive quarterly profit, a string dating back to 1991.

It won't be the first time that the USA's leading discount carrier has earned money while a financial crisis threatened other carriers' survival.

What is its secret?

There are lots of factors, but easily the most important is that Southwest is the champion oil price hedger among airlines worldwide.

Using some simple and some complex investment strategies, Southwest has for a decade locked in the prices it pays for large amounts of jet fuel months and even years ahead of time. Its success at that has protected it from run-ups in crude oil prices and dramatically cut its fuel expenses. Since 1998, it has saved $3.5 billion over what it would have spent if it had paid the industry's average price for jet fuel. That's equal to about 83% of the company's profits over the last 9 1/2 years.

On the spot market, jet fuel sold at an average price of $3.95 a gallon for the week ended Friday. A week earlier, the average price was $4.10. American Airlines paid an average $3.17 a gallon last quarter. Delta, $3.13. And Southwest? Its second-quarter average will be disclosed today, but its recent estimate was about $2.35 a gallon.

That advantage will narrow, and perhaps disappear, as Southwest's $5 billion in fuel-hedging contracts expire over the next four years. With crude oil prices having fallen more than $20 a barrel the past two weeks to $124, the risk of a plunge in prices is higher, the odds of another steep, fast run-up more uncertain, and Southwest's hedging profits harder to sustain.