Matt LeBlanc and Jennifer Aniston are two of the show's stars

Up to 50 million people are expected to tune in to NBC on Thursday as Friends draws to an end after 10 years.

The sitcom will bow out with a one-hour special, followed by its six stars appearing on the Tonight talk show.

Ad slots for this year's Super Bowl game were sold for $2.3m (�1.3m), while Oscars space went for $1.5m (�835,000).

Some companies booked slots for the Friends finale a year in advance, and will use them to introduce expensive new adverts.

The cast will be appearing on Oprah Winfrey's show on Friday

"This is one of those rare media events," said Charlie Rutman, president of advertising buyers Carat USA.

"It's a programme that has captured a generation and a lifestyle for 10 years. It's become more than just a television programme."

But Bob Flood of advertising buyers Optimedia doubted the Friends finale would have the same audience reach as that of the end of Cheers and Mash.

"This is a much more competitive landscape," he said.

Huge audience

"But clearly, NBC is putting a lot of promotion behind this to ensure that it's going to be a ratings success."

NBC is capitalising on its potentially huge audience by packing its schedule with Friends-related programming.

There will be a one-hour highlights show preceding it, while a two-hour Dateline NBC special will be aired on Wednesday.