An estimated 20 per cent of Fox's Nascar inventory for remaining broadcasts this season is unsold, media buyers say. The network recently turned over to its affiliate stations four 30-second commercial spots per race that it has been unable to sell nationally, giving local marketers a chance to associate with the popular sport. The main reasons for the sales problems: Fox has refused to cut prices in the slumping TV ad market, and Nascar sponsors have been reluctant to overspend.

"We're going to maintain the integrity of our marketplace and hope that pays off long term," says Mr Jon Nesvig, president of sales for Fox Broadcasting, a unit of News Corp. Advertisers, he says, must "realise that a product of this quality and exposure comes with a price."

Nascar's TV draw has been a success story, so far. Six races broadcast on Fox through March 18 averaged an audience of 11.8 million viewers, up 37 per cent from last year's 8.6 million average on Walt Disney's ABC, Viacom's CBS and General Electric's NBC. Nascar has posted higher ratings so far in 17 of the nation's top 20 media markets. Plus, the highly sought audience of men 18 to 34 years old is up more than 50 per cent, according to Nielsen Media Research figures.

National media attention has helped, as has broadcast stability. Nascar for the first time has a single television deal, allowing it and the networks to promote the sport heavily nationwide. In the past, individual racetracks negotiated individually with a variety of broadcast and cable networks. The first half of the Nascar season, which ends June 24, belongs to Fox and its cable networks. The second half will be on NBC and AOL Time Warner's TBS. Those two networks jointly are paying $1.2 billion for six years.

Facing a $200 million-a-year Nascar price tag, NBC and Fox have taken an aggressive stance towards advertisers. Media buyers say prices for some 30-second network spots have more than doubled from last year, to around $125,000 for a typical race and $200,000 for a premium event such as the Daytona 500.

More important, however, has been Fox's line-in-the-track stance on advertisers' participation in broadcasts. A Nascar race, its cars tattooed with corporate logos, already amounts to a three-hour moving billboard. So Fox pushed companies to pay for seasonlong commercial packages and reserved on-screen features - such as a new ticker that tracks race standings and cameras mounted inside drivers' cars - primarily for sponsors who buy commercial time.

Fox even is selling title sponsorships to the broadcast of races that already have sponsors. For instance, Fox promoted its March 11 broadcast as "Winston Cup racing live from Atlanta, presented by UPS" - major advertiser United Parcel Service - rather than as the "Cracker Barrel 500," named for the racetrack sponsor, CBRL Group's Cracker Barrel, which didn't buy commercial time. Contractually, Nascar broadcasters once per hour have to refer to races by the name of the track sponsor.

"They've stuck to saying that people who do not spend money on the broadcast will not get the broadcast exposure," says Mr Jon Stimmel, senior vice- president for national broadcast at Interpublic Group's Lowe Lintas & Partners. Fox executives say the network's ad strategy hasn't affected editorial coverage of races, such as shots of cars or interviews with drivers.

Some longtime Nascar sponsors and advertisers have balked at the higher prices. Ashland's motor-oil unit Valvoline, which used to regularly pay for commercials and in-car cameras, didn't buy a single ad on the first five Fox broadcasts. "There are ways to get our message out that are more cost-effective," says Mr Barry Bronson, Valvoline's communications director.

Fox could lower prices to sell its leftover inventory. But it isn't doing that because the impressive ratings suggest it will be able to raise rates for Nascar next year. Plus, handing over some commercial time to affiliates is a goodwill gesture at a time when the market is slumping. "We love the spots and they've sold aggressively," says Mr Kevin O'Brien, president and general manager of Fox affiliate KTVU in San Francisco.

Still, Fox's decision ultimately reflects the weak marketplace. "They wouldn't be giving back the inventory if they could sell it," says Mr Bill Koenigsberg, president and chief executive of ad-buying agency Horizon Media.

The Wall Street Journal