Updated from 7:28 a.m. EDT

With consumers benefiting from lower gas prices, expectations are on the rise for September's retail sales results, despite an early disappointment from

Wal-Mart

(WMT) - Get Report

.

The bulk of U.S. retail chains are expected to release September sales figures Thursday morning, and the numbers should be solid. Ken Perkins, president of research firm RetailMetrics, says expectations for his firm's aggregate same-store sales index have climbed 60 basis points in the last week thanks to optimism on Wall Street about a strong back-to-school season for teen-apparel retailers and department-store chains.

Perkins' overall index, tracking analysts' expectations for results from more than 70 major retail chains, predicts an increase of 3.7% for September, compared with a 4.1% gain recorded in the same month last year. The index tracks same-store sales, or comps -- a closely watched retail metric that gauges sales at stores that have been open for at least a year.

"Looks like it could be one of the best months of the year so far," says Perkins. "Back-to-school got off to a real slow start in August, but things picked up throughout the month. That momentum seems to have spilled over into September. Labor Day-weekend sales were strong by most accounts, and ready-to-wear fall sales have been strong as cooler temperatures have come into play."

If the optimism proves well-founded, that should bode well for the all-important holiday selling season, and it would also challenge the widely held view on Wall Street that the slumping housing market will cause consumers to go on a shopping diet.

"Obviously you have the big bonus of plummeting gas prices, which appears to be having a big impact on the consumer psyche, making people feel better about their overall economic plate," says Perkins. "Also, the job market has continued to hold very solid here throughout September."

On Tuesday, crude oil futures dropped $2.35 to close at $58.68 a barrel, their lowest close since July 2005. The price of crude has now fallen 25% from its July 14 high of $78.40.

Excluding a relatively disappointing forecast from Wal-Mart, which said over the weekend that its September comps would come in at the low end of its guidance at 1.8%, RetailMetrics is forecasting a 4% increase for its index.

On Wednesday, Wal-Mart tempered its view even further, projecting a 1.3% comp increase for the month.

But

Kohl's

(KSS) - Get Report

strong outlook Tuesday helps to ease concerns that Wal-Mart's slowness was felt throughout the sector. The midmarket department-store chain posted a 16% increase in September comps, blowing away Wall Street's expectations.

"All regions of the country experienced double-digit comparable-store sales increases for the month," said Kohl's in a press release. "We are experiencing healthy increases in both transactions per store and average transaction value."

Jharonne Martis, an analyst with Thomson First Call, says Kohl's results reflect the broad strength that is expected to show up in results from department stores and teen retailers. Teen-apparel chains like

Abercrombie & Fitch

(ANF) - Get Report

and

American Eagle Outfitters

(AEOS)

, along with other discretionary retail chains, are expected to lead the sector with an overall same-store gain of 6.5%.

"That's pretty high, and it suggests that consumers are not holding back," says Martis. "There are no real signs of any weakness coming from the sector."

The only segment in the industry headed for a comp increase of less than 3% is specialty stores, which are expected to show a 0.1% same-store sales rise. That space is being weighed down by perennial laggards like

Gap

(GPS) - Get Report

,

Pier 1 Imports

(PIR) - Get Report

and

Sharper Image

(SHRP)

.

Gap is expected to continue its string of negative monthly comps with a 6% decline in September. That performance would call into question whether the specialty empire can turn around its fortunes in the back half of 2006 as it strives to bring customers back to its stores.

"Gap is starting to do better," says Morningstar analyst Joe Beaulieu. "They have more of a marketing message these days, especially on the women's side of their businesses. The fact that they're back to advertising on television shows they have some confidence that there's merchandise in the stores now that their customers are going to want."

Beaulieu also says Wal-Mart's troubles will prove to be temporary.

"Wal-Mart is in transition with their business," he says. "They're trying new store formats to attract more affluent customers. Overall, retailers are still facing headwinds, but those chains that are managing to sell desirable merchandise in their stores should continue to do well, while those chains that aren't on top of what consumers really want will probably start to drop off soon."

The sharp slowdown in the U.S. housing market sowed fears in the stock market over the summer that weighed on retail stocks. But the S&P Retail Index has rallied 10.4% since the start of September as investors embrace the notion that consumer spending will surviving housing's slump.

"I'm still concerned about the housing market and its impact on consumer spending, but people seem to be shrugging that off at this point," says Perkins. "If housing prices go into free-fall when we go into the winter months with high inventories of unsold houses in the slow selling period, it'll be interesting to see if prices really do bite into spending. If they start to come down significantly, then that should trump whatever energy prices are doing by far in the minds of consumers."