Even Alan Horn, president/COO of Warner Bros, could not have predicted quite the mega box-office success of The Dark Knight, which is nearing the $1bn threshold. 'We knew the film was good. We didn't know if we're going to have a picture that does $300m or $900 million,' he says. 'This kind of business is extraordinary. It was all the factors that burst into full bloom here.'

Even though no tentpole is a sure thing, there were a number of signals that prepared Horn and his colleagues for the best possible outcome. 'Batman Begins primed the pump by reintroducing the Batman character to the international market, and it also had enormous home video success. The Dark Knight re-teamed most of the same elements, including Christopher Nolan and Christian Bale.'

The film also became a news event following Heath Ledger's tragic death in January. Horn continues: 'An important component in any of these kind of movies is to have a worthy adversary or villain. We had Heath Ledger's special interpretation of the Joker. When he passed away, the studio had to handle that with tremendous sensitivity, and we worked with his family on that. Heath had done something special with this role, and that would have had attention even if he'd not passed away.'

The film's Imax content added to a record-breaking run on Imax screens, which Horn says was 'important but not critical'. What was critical, though, was a family-friendly PG-13 rating. '[Throughout production], we had to be sensitive to the rating,' Horn says. 'We all supported Chris Nolan's vision within the constraints of a PG-13 rating. It couldn't be so dark that we'd end up with the R rating.'

The Dark Knight now stands at $992m worldwide, helped by a whopping $528m in the US (number two of all time, behind only Titanic's $600m). The film could get a further boost with awards season attention and corresponding re-release if appropriate.

And yet this dark story of a tormented superhero is wildly different from another international hit of 2008, the unabashedly light musical romp Mamma Mia!: The Movie, which has taken over $414m internationally.

Tim Richards, CEO of UK exhibitor Vue Cinemas, notes the two films, while 'diametrically opposed', both drew in those crucial repeat viewers that turn a film from a hit into a phenomenon. As Richards says: 'If only we knew how to bottle a blockbuster... '

INTERNATIONAL MONEY, MONEY, MONEY

Unlike The Dark Knight, Mamma Mia! was not a runaway hit in the US but did a solid $144m. Universal Pictures International (UPI) president David Kosse notes the number is not that representative of its international success.

The film opened on July 3 in the UK and expanded elsewhere in Europe before its July 18 US opening. Leveraging the star power (led by Meryl Streep), the success of the original stage production (seen by over 30 million people) and the enduring success of Abba's music, particularly in Europe, Mamma Mia! has now become the biggest UK film ever in its home market, standing at $105.8m (£65.5m) and it could even overtake Titanic as the largest film at the UK box office. Titanic grossed $111.5m (£69m).

Kosse believes it was important not to push for a day-and-date launch worldwide. 'If you try to convince everyone ahead of time that this is going to be a $500m hit, that's hard,' he says. 'But we made it a massive success in the first five or six territories and then the others could start to get on board and see the potential.'

The strategy worked. Mamma Mia! has become the top film of the year in about 15 markets, from Iceland to Germany to South Africa. One of the few places it didn't work was the United Arab Emirates. 'Maybe those audiences weren't particularly keen on the story of a woman with three possible fathers,' Kosse speculates.

Asian audiences do not always embrace musicals but it did very well in places such as South Korea, and UPI expects to add a further $50m-$55m in Japan when the film opens there in late January 2009.

The film campaign worked around the world with slight tweaks for local sensibilities. 'In markets that were less musical-focused, we pushed it as a romantic comedy with music, and where they do like musicals we pushed it as a musical with romantic comedy elements,' Kosse says.

UPI was also able to offer a second experience with the same film: the sing-along screenings launched in late August. 'That was perfect timing, it was just at the point it could have started to slide, and then it had new life,' an executive at another distributor points out. Mamma Mia! is still playing in quite a few markets, including the UK, and the latest push is group ticket sales for Christmas parties and outings.

WHERE AND WHEN

The international success of Mamma Mia! is testament to how important the overseas market is for major studio films (Mamma Mia! is a US-UK co-production). Paramount Pictures International (PPI) president Andrew Cripps says: 'Four to five years ago, films internationally did maybe 50% of the overall box office. Now that's at 60% and a lot of movies can do 70% or 75%. We'll continue to see the international marketplace outpacing US growth. It will become even more important.'

In fact, it was international performance that drove Warner Bros to push back the fifth film in the Harry Potter franchise, Harry Potter And The Half-Blood Prince, from November 2008 to July 2009. 'We were aware we didn't have as strong a tentpole line-up in 2009 as compared to 2008,' Horn says. 'Especially internationally, when we don't have the international distribution rights to films such as Terminator Salvation and Watchmen (which Warner Bros will release in the US).'

The Dark Knight's massive haul was also a factor in the Potter decision. 'If The Dark Knight hadn't done so well we wouldn't have been able to beat our 2008 goals (without Potter); all of a sudden we had the flexibility with 2008 and 2009,' Horn explains.

The UK, in particular, has become the key non-US territory for Hollywood films. Japan can deliver higher grosses, but the UK has emerged as the most consistent predictor of an international hit. One person with a close eye on UK performance this week is Mark Zucker, president of distribution at Sony Pictures Releasing International (Spri), which just set new records for an opening weekend in the UK with the 22nd James Bond film, Quantum Of Solace.

Bond always plays well in the UK and northern Europe; 71% of Casino Royale's grosses were outside North America, where it took $167m. (It took $106m in the UK.) So launching early in the UK means that the UK records can build buzz elsewhere. 'Americans like to hear the news that a film has set records in the UK,' Zucker says. 'Especially with the credit crunch, Americans will be more willing to go see a proven product.'

Quantum Of Solace moves into a further 57 territories this weekend before opening in North America and Mexico on November 14, Australia on November 19, Spain on November 21 and Japan on January 24, 2009.

Zucker says that the action-centric story of Quantum should play well in Asia and better than most past Bond films in Latin America. Also, Quantum has a November 17 release in piracy- ridden China (Casino Royale had to wait for a January launch.) 'In China, we'll be in more theatres than any Hollywood film ever - about 1,400 screens,' Zucker notes.

ELEMENTS FOR A HIT

Just having a good movie isn't enough, of course - a project needs to have that huge 'want-to-see' factor to drive up mega box-office. That can be spurred by established brand awareness from past films, books or graphic novels; a must-see news angle; an A-list cast; or, when the stars align, all of the above. 'You've got to have some form of pre-established awareness to get huge box-office success,' says PPI's Cripps, who had a big hit this summer with Indiana Jones And The Kingdom Of The Crystal Skull (now at $467m internationally plus $317m domestically).

Getting the word out about films early is key. 'The earlier the better with films in that blockbuster category,' Cripps says. For instance, Paramount has JJ Abrams on a multi-country promo tour now showing 20 minutes of Star Trek to partners, exhibitors and key press ahead of its May 2009 launch. And toy manufacturer Hasbro has already started promoting a new line ahead of PPI's release of GI Joe in summer 2009.

Vue's Richards notes: 'We also start at a very early stage.' Early work is starting to pay off with new records being set for pre-opening ticket sales for films including High School Musical 3: Senior Year and Quantum Of Solace.

At the other end of the timeline, keeping a film playing long enough to keep driving word of mouth is important. For Mamma Mia!, persuading exhibitors to keep the film booked for a long run was not an issue in most cases, Kosse notes. 'If you keep the film on longer, usually the terms get better for (the exhibitor),' he says. 'And this is a good demographic for them to get into cinemas, both older and younger than the typical multiplex viewer.'

Of course, it is possible these films have achieved such big numbers precisely because the market was not too overcrowded. Richards says: 'In the summer of 2007, we were taking off good movies even when there was still demand for them to make room for the next good movies. Summer 2007 was the best in years and now this summer is up 12.5% on that.'

The enduring question is how to make a film that will join the billion-dollar club. Warner's Horn says: 'The lesson this underlines is that if you're going to make an expensive, big-budget tentpole movie, it's important that it plays across all sectors: young, old, male, female, US and international.'

Above all, the industry - even when giddy with a mega-hit - tries to remember it is never an exact science. Kosse says: 'Mamma Mia! had the elements to do breakout business, but it's up to the gods.'