Keeneland's September sale, which starts its 14-session run on Monday in Lexington, will test the yearling marketplace at every level. The biggest auction of its kind in the world, with more than 5,000 horses catalogued, it has blue-blooded stock that will attract Middle Eastern royalty and yearlings with modest pedigrees that will appeal to trainers at small racetracks.However, there is widespread concern that the huge supply of yearlings will exceed the demand. Results of earlier auctions this year indicate there are more horses available than there are buyers. Fasig-Tipton sales in Kentucky and Texas had larger catalogues and suffered downturns while the Ocala Breeders' Sales Co.'s August auction also followed the same trends.Another worry is the impact of Hurricane Katrina, which devastated New Orleans and other cities along the Gulf Coast.Before the storm, Keeneland's director of sales, Geoffrey Russell, did not think the increased number of horses in the September sale would be a problem. Now, he's not so sure."New Orleans is a very important city in the economy of North America, and what happened there is going to have a ripple effect on everything," he said. "New Orleans is a key port for import and export, and now it's closed down. And we're having to pay $3 a gallon for gas. People buy horses with discretionary income, and if the economy goes into a lull, the discretionary income decreases."Keeneland's seven books list more horses than ever before, 5,110. The total is up 4.5% from the sale's previous mark of 4,891 that was established last year.On a brighter note, the Fasig-Tipton's select Saratoga auction had a smaller catalogue and its average and median prices improved, suggesting that demand remains high for yearlings of the highest quality. That's good news for the first two days of the Keeneland sale, which are select sessions."I've never seen a stronger catalogue in terms of pedigree," said William S. Farish of Lane's End Farm. "It's a very strong catalogue, and it should be an awfully strong sale."Monday and Tuesday's select sessions have a lot to live up to. In 2004, select records were established for average and median while the gross revenue reached its second-highest level ever. A Storm Cat – Welcome Surprise colt became highest-priced September yearling ever when he sold for $8 million.The figures for last year's entire September auction included a gross that was the highest ever for any Thoroughbred auction in the world. The average and median were all-time September highs.All sessions for this year's sale, which runs through Sept. 26, begin at 10 a.m. (EDT). There is a break from selling on Sept. 16.