Shane Kim, corporate vice president of Microsoft Game Studios, said the success Halo 3 was an essential element in the competitive console market.

He said: "Halo 3 is the biggest franchise for Xbox. The game is going to drive a lot of Xbox 360 sales and Xbox Live subscriptions this Christmas."

Boost sales

Microsoft needs Halo 3 to boost sales of the Xbox 360; despite investing billions of dollars into the Xbox project it has yet to see any meaningful profitable return

"It's far too early to say what the financial return will be for our investment," Mr Kim told the BBC News website.

Microsoft hopes to make a profit on its Xbox in this financial year.

"If we can't make a profit in the year Halo 3 comes out, then when will we?" said Mr Kim.

More than a million people have pre-ordered the game but that is not preventing thousands of gamers from queuing outside shops to get their hands on the title as soon as possible.

Concluding part

Halo 3 is the concluding part of a science fiction trilogy which tells the story of a super soldier, called Master Chief, who is leading the fight to save humanity from an alien collective, called the Covenant.

The game has become a major entertainment franchise in recent years - with spin-off games, clothing, novels and action figures all available.

The Lord of the Rings director Peter Jackson is working with Halo's makers, Bungie studios, on a series of Halo-related interactive episodes.

He has also agreed to produce a movie based on the Halo series, which is currently on hold following financial wrangles over the cost of the film.

Web reviews of the game have begun to emerge with most posting very high scores.

Game site Eurogamer wrote: "Hype machine aside... what we find in Halo 3 is quite simply this - the best game yet in one of the best FPS (first person shooter) franchises of the era."

All three of the leading games consoles rely on exclusive franchises to drive sales. PlayStation 3 has titles such as Metal Gear Solid 4 and Killzone 2, while Nintendo has Metroid Prime 3 and Zelda.

Microsoft has spent a reported $10m (£5m) on promoting the game, with a series of costly TV adverts, as well as signing deals with food and drink firms in the US.

Most pressure

The game goes on sale in Europe on September 26, with a UK launch on Tuesday night at the Imax cinema in London.

For Bungie, the game's release is the culmination of three years work.

Brian Jarrard, Bungie's director of franchise and community affairs, said the company had not felt under pressure from Microsoft, which owns the studio.

"We feel the most pressure ourselves. It's always been about driving ourselves to do great work. For the most part we don't feel the pressure from Microsoft executives breathing down our necks.

"The fan's expectations are incredibly high. We gave them a bitter sweet ending at the end of Halo 2 and we're pretty confident they will be happy with Halo 3 and that it was worth the wait."