There will be three more series of Emmy-winning TV show Lost before it finally ends in 2010.
Evangeline Lilly plays Kate Austin, one of the central characters
A "highly-anticipated and shocking finale" is being planned by TV network ABC, which acknowledged viewers may drift away unless the drama concludes.
Each series will be 16 episodes with no mid-season break, following complaints the last series was divided in two.
The desert-island programme, which stars Evangeline Lilly and Matthew Fox, follows the survivors of a plane crash.
They are stranded in a mysterious location and must come to terms with the other inhabitants of the island as well as the isolation of their new home.
"Due to the unique nature of the series, we knew it would require an end date to keep the integrity and strength of the show consistent throughout and to give the audience the pay-off they deserve," said Stephen McPherson, the president of ABC Entertainment.
Two of the people responsible for the programme - executive producers Damon Lindelof and Carlton Cuse - have agreed to remain until the end of the run.
They said in a joint statement that they had always thought of Lost as a show "with a beginning, middle and end", and hoped fans would be happy knowing that it would now "play out as we've intended".
Lost was once watched by more than 20 million viewers each week in the US.
However, the most recent series drew audiences of about 12 million in its Wednesday evening timeslot.
Viewing figures in the UK have also slipped since it moved to Sky from Channel 4.