Executives at US television network NBC are trying to calm advertisers' nerves in the face of double-digit falls in ratings figures for the new season.

The broadcaster has been shaken from the ratings tree after more than ten years at the top and finds itself in a situation where, it is whispered, it might have to give away 'make good' time to advertisers if the decline cannot be halted.

Overall, NBC is down 12% in total viewers and 16% in the 18-to-49 age category, the most attractive audience to advertisers.

The most alarming slide in ratings figures is on Thursday nights, traditionally an NBC fortress when airtime is at top dollar.

The network had raked in advertising commitment to the tune of $2.9bn (€2.2bn, £1.5bn) for the 2004/5 season with a 'famous last words' promise from TV Group chairman Jeff Zucker in May : "Our Thursday night is going to be even stronger."

The passing of top shows Friends and Frasier, both of which attracted an upscale audience, is partly to blame for the viewing fall-off. The spinoff, Joey, although strong, is not the same ratings heavy hitter as its illustrious parent.

And to give credit where due, NBC's rivals have produced some promising contenders this season, including ABC's Desperate Housewives and the continuing success of CBS's CSI: Crime Scene Investigation franchise.

However, NBC chiefs are putting a positive spin on their predicament. Says Randy Falco, president of the Universal Networks Group: "We are nowhere near being in a make-good situation."

The broadcaster has some new shows to be launched mid-season which it hopes will turn the tide – and of which media-buyers are approving. But, says SG Cowen & Co analyst Lowell Singert: "NBC's chances of regaining the lead appear to be limited."

Data sourced from Wall Street Journal Online; additional content by WARC staff