ER is the only show more popular than Friends

The programme has had a history of salary dispures since it started in 1994, when the actors were paid just $1,600 (�1,000) an episode. In 1996, the cast threatened to go on strike unless they received pay increases.

Last year Warner Bros paid the Friends stars a Christmas bonus of $200,000 (�126,000) designed to keep them with the series.

As well as being a worldwide hit, Friends has helped NBC to dominate Thursday nights on US television, attracting an average of 23.5m viewers each week.

It is the country's most-watched comedy, and the second most-watched show overall behind medical drama ER - which is also made by Warner Bros for NBC. It has also held its popularity - in contrast to steep declines shown by other NBC shows.

NBC recently paid Warner Bros $13m ($8.2m) per show for three more seasons of ER. The Friends deal could be worth a smiliar amount on a cost-per-hour basis, earning Warner Bros $10m (�6.3m) per hour.