Delta Air Lines (NYSE: DAL) was on the upswing Monday after the firm raised its forecast for third-quarter margins. The airline issue now expects operating margin of 3% to 4% for the current quarter, compared to its midsummer outlook of 1% to 3%. Third-quarter fuel prices are now expected to average $2.14 per gallon, down from a prior prediction of $2.17.

The update comes courtesy of a regulatory filing, wherein Delta noted that many of its financial metrics are improving on both a sequential and a year-over-year basis. Load factor for September and October is pegged at 82%, narrowly above last year's level. Meanwhile, revenue per available seat mile is expected to decline in the third quarter, but less so than in the second quarter.

It's a pattern that's been all too familiar in the oil market these past few months: the price of oil moves slightly higher, but then can't sustain its increase and the rally fails, usually with oil closing lower at the end of the day.

What's causing it? Energy traders and economists will tell you that the price decline is being driven by slowing oil demand growth in emerging markets, combined with real, year-over-year demand reduction in the world's biggest market, the United States.

Investors exit oil

But that's not the whole story behind oil's stunning drop from $147 to the $60-per-barrel-range, so says Energy Trader Jim Dietz. Dietz who argues that the global reduction in the availability of leverage -- money borrowed for use in trading -- has taken a considerable amount of the buying pressure out of oil, as well as other commodities.

"We clearly are not seeing as many hedge funds and investment funds establishing positions in oil, and the ones who are in the market are establishing smaller positions," Dietz said. "As a result we rarely see any more powerful moves to the upside with powerful momentum characteristics. I'm not saying hedge fund buying is the only reason oil hit $147 this summer, but they certainly played an important role."

Barron's takes a look at what could be a bad omen for the future of the stock market (subscription required), at least in the short-term: "Even after a recent drop, margin debt remains within spitting distance of the all-time high it hit in July, and 43% higher than it was a year ago. At a current level of 2.4% of the market's adjusted market cap, margin debt is 3.4 times its 62-year average.

Why worry? For starters, high margin debt could result in widespread margin calls in the wake of rapid market decline, leading to a domino effect prolonging the market decline. For evidence of this phenomenon, please see The Great Crash of 1929.

But high margin levels are also a very bearish contrarian indicator. They show that many investors are maxed out -- even if they wanted to, they simply couldn't buy more stock -- they're already borrowing at near-record levels to do just that! New money is often a prerequisite for a bull market, and already-high margin levels could make it hard for new money to come in. The bullishness of the investment community is a very bearish indicator for contrarian analysts.