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The one-hour special - airing at 9pm on NBC - is one of the most anticipated episodes of a TV series since Seinfeld finished in 1998.
Among the outcomes fans will be waiting for is whether Ross and Rachel finally end up back together.
30-second advertising spots during the programme are being sold for around $2m (£1.1m) each, a record figure for a sitcom and putting it on par with the annual Superbowl.
Production company Warner Bros. are hoping to cash in further by releasing the final episode on DVD in five days' time, containing unseen scenes from the finale, behind-the-scenes footage and the original pilot episode.
The finale will air May 28 on Channel 4 in the UK.
