By Toby Poston
BBC News business reporter
Big Brother 7 should be the biggest money-earner yet
The seventh series of Channel 4's Big Brother is set to be the biggest ever.
It will have the largest ever team of contestants, will run for longer and have more programmes built around it.
And it will probably be the biggest money-spinner yet for both the broadcaster and the production company making it, Endemol.
Big Brother virtually invented modern reality TV, and it is a flagship of both companies' operations.
It is the top programme format for Endemol, which has sold it to 37 countries around the world.
In the UK, Big Brother's success has helped make the country Endemol's top earning region, with revenues growing 18.4% in 2005.
The company turned over £614m last year and income from Big Brother related activities is thought to make up just under 20% of that.
For Channel 4, the importance of Big Brother is a little harder to quantify.
It is understandably coy about how much it earns from the programme, partly because many in the industry argue that, as a broadcaster with a public service remit, it shouldn't produce such programmes anyway.
And because it has no shareholders, all the money Channel 4 makes from Big Brother gets pumped back into producing innovative comedy, expensive dramas and areas such as news and current affairs - none of which attract anything like as many viewers.
Advertising revenues are the hardest to quantify. TV time is bought in bulk in advance, so an advertiser or TV buyer cannot usually pick a particular programme in which to place their ad.
Millions of Big Brother fans will vote to evict contestants
They buy space on a particular channel, at a price based on the size of their order and the audience demographic that Channel 4 can deliver.
Big Brother deliver huge audiences, nearly 8 million for the final night of Big Brother 6 last year, its biggest audience of the year.
It also delivers a large number of 16-34 year old viewers, who watch less TV than older viewers and are therefore more expensive to reach.
The right viewers
Big Brother's huge audiences have helped keep Channel 4's share of the viewing audience stable over the past five years, while other broadcasters like ITV and the BBC have lost viewers to a host of new non-terrestrial channels.
So it is probably safe to assume that Channel 4's advertising revenues have probably held up better than ITV's in recent years.
"TV deals are based on the previous year's viewing figures, and you need proven properties that advertisers know will deliver," says Adam Turner, broadcast director at media agency PHD.
Big Brother 7 will have four programmes on Channel 4's digital channel E4. Big Brother will deliver the audiences and ad revenues that will more than make up for the channel's move from being a subscription channel to a free one.
Channel 4 can also sell ad space online. With eight million unique users last year, the huge Big Brother website is an attractive proposition for pay per click advertisers.
This year sees the launch of a free internet video service, which will provide 12 free clips per day, each of which will have a 30-second advert at the start.
Bookmakers say they don't earn much from Big Brother betting
Perhaps the single biggest advertising contribution comes from Carphone Warehouse, which first sponsored Big Brother back in 2004 as a branding exercise for its new TalkTalk landline telephone service.
Industry experts estimate that this year's sponsorship deal could be worth up to £4.5m.
Ringing up a profit
But what about the humble viewer?
Despite the promotion of free services, Channel 4 is still deploying a range of ways to empty viewers' pockets.
The most prominent is the voting on who gets evicted from the show. Whether by telephone or text message, each vote brings in at least 50p even before the telecoms operator's cut is added on top - although 10p of this goes to charity.
Channel 4 is reticent about the number of votes it receives, but gives out figures for the final eviction night.
There were 6.4 million votes on the last night of Big Brother 5, adding up to a cool £3.2m, although this will have been shared with Endemol and the company running the voting system.
Viewers will also be invited to ring or text in to spin-off programme Big Brother's Little Brother with their comments and questions, at a cost of 25p.
Finally, they will be able to pay £7.99 to subscribe to live screenings of the Big Brother action on their computer, or pay for text alerts on their mobile phone.
But some viewers are making money off the programme, as well as paying for it.
Bookmakers are predicted to take up to £10m in wagers as people bet on evictions, top male, top female and whether contestants will walk out - but they don't expect to make much of a profit.
"It is guesswork from our end, we know as much as the public," said a William Hill spokesman.
"When it is racing or football, punters will do very well to beat our experts on a regular basis, but last year we barely broke even."
Jade Goody has been one of Big Brother's biggest earners
Perhaps the biggest Big Brother earners are some of the contestants lucky - or crazy - enough to enter the Big Brother house.
Take Jade Goody, a star performer on Big Brother 3.
According to one tabloid newspaper, since then she has earned over £1m from newspaper and magazine deals, TV appearances, workout videos, playing the Wicked Queen in a panto, special appearances and an autobiography.
Not bad - especially since someone else actually won that year.