Matthew Fox has been a star of Lost since the first series
Viewers of the fifth series of Lost will not know where or when the action is set, the show's producers have said.
Talking at arts and comic book convention Comic-Con, they revealed they would play around with the show's flash-back and flash-forward formula.
Executive producer Carlton Cuse said: "We have something new this year. We're going to mix it up."
Lost, which centres on a group of plane crash survivors, won a Golden Globe for best drama series in 2006.
Executive producer Damon Lindelof said "the flash-forwards were a bit limiting" during the last series of the programme, as they could only show a group of six survivors who the audience already knew had escaped the crash site.
"We could only focus on the Oceanic Six because we didn't want to reveal certain things - like Desmond getting off the island," he said.
"When season five starts, you won't know when or where you are. And the way we tell stories will be different too."
"Also we have the guy who makes the whooshing sound for us and we would not want to put him out of work."
US network ABC has allowed the producers to set an expiration date for the show, which will draw to a close after the sixth series.
Cuse said: "For us it was a huge advantage to get an end date to the show and that really allowed us to turn a corner.
"We knew exactly how much story we had left. It really invigorated series four and it's been very exciting as we plan series five now."
Lindelof told the 6,500 assembled fans: "You will be rewarded for hanging on all the way to end of series six. We think that we have a lot of cool stuff from here on out."
Lost has just been nominated for an Emmy for outstanding drama series, ahead of the award show in 21 September.
It is broadcast by Sky One in the UK.