Letterman could outlast Leno in late-night TV

Late night host David Letterman has signed on for four more years with the Late Show on CBS, the Hollywood Reporter said on Thursday.

If he stays with show to the end of his contract in 2010, he will outlast Jay Leno, who has the rival slot on U.S. network NBC.

Leno will be host of the Tonight show until 2009, when Conan O'Brien takes over.

Leno and Letterman have been rivals in late-night television since 1993, when Leno joined Tonight and Letterman moved to CBS.

Letterman, 59, has had health problems in recent years, including heart surgery in 2000 and shingles in 2003.

He also is low man in the ratings, drawing 4.16 million viewers, compared to 5.71 million for Leno.

That has led to speculation he would step down.

O'Brien, who he will compete against beginning in 2009, took over Letterman's NBC show in 1993.

NBC was apparently so keen not to have O'Brien jump ship that it signed him on to host Leno's show years down the road.

All three hosts try to win late-night audiences with humour and a selection of famous and not-so-famous guests.

Letterman is known for his sometimes quirky skits, while Leno has a more mainstream style.