For a film that's been roundly maligned by critics, and seems to have as many people who love it as hate it, Transformers: Revenge Of The Fallen is showing little sign of slowing up at the global box office. Off the back of another strong weekend for the film at the US box office, its current take in the States stands at a bewildering $339m. To put that into context for the year, it's by some distance at the top of the box office chart, with second place Up trailing by some way behind at $273m. And Transformers 2 still has plenty of fuel in the tank.

It's a fair guess now that the film should pass the $400m by the time its business in the States is done, and it's already surpassed the $319m that its predecessor stumped up. What's more, the worldwide take is measuring up too. More often than is publicised, films that do major money in the States don't always enjoy quite the same level of success overseas (it happens the other way round too, of course), but with Transformers 2 now crossing the $700m when international receipts are counted, it should be the biggest film of the year.

That is, of course, unless Harry Potter can pull out something special. Early reports suggested that pre-sales for the sixth Harry Potter film were ahead of those for Transformers, and when Harry Potter And The Half-Blood Prince finally opens on Wednesday, we're expecting to see a dramatic box office take. There's been a two-year wait for Potter fans to see the film, and it's also the last major live action family movie of the summer blockbuster season. You can expect a massive opening here, although whether it measures up to Transformers 2's staggering first week receipts remains to be seen.

For, with Transformers 2 careering towards that $400m mark in the US, Harry Potter is going to have to climb over a few obstacles to beat it. Firstly, it's going to have to outperform every Potter film to date, with the highest grossing in the franchise still the first, way back in 2001. That made $317m in the US and the last film, Order Of The Phoenix, sat at $292m.

It's not as if Potter has a clear run in the same way  Transformers had either. As the school holidays begin, the number of films fighting for the family dollar increase. Next week, Disney rolls out guinea pig epic G-Force and Fox has Aliens In The Attic after that. Perhaps such weighty competition is why Sony has kept its Cloudy With A Chance Of Meatballs out of the firing line, sitting instead in September.

The likelihood is that, despite the power of Hogwarts, Harry Potter And The Half-Blood Prince will top out at best at the $350m mark, and that's if it has a really good day at the office. The early reviews, to be fair, are quite ecstatic (including our own), and word of mouth will do no harm.

But this is still, no matter how you look at it, the summer of the Transformers. And that's why Paramount is quite so keen to lure Michael Bay back to churn out another robot mash in two years' time...