ask: Has the basic concept of a movie star become something of an anachronism?"

The studios certainly think so. They are increasingly relying on high-concept 'franchise' films that don't depend on big stars. These include enormous hits like Iron Man, which has just taken $200m worldwide in its first weekend, Spider-man, Harry Potter, Batman and the upcoming 2008 releases Wanted, Wolf Man and Death Race. The other big money-spinners these days are cheap comedies like Knocked Up and Forgetting Sarah Marshall from producer-director Judd Apatow, which don't need big stars.

"What more and more studios are saying is, 'Let's find a concept we can market and once we have that, then we'll get the best actor who can fit that'," says one agent. Of course some of these franchise pictures, like Pirates of the Caribbean with Johnny Depp and now Iron Man with Robert Downey Jnr, are boosted by their star actors. But the new Hollywood rule is that outside these franchises even such huge stars as Depp have little drawing power any more.

"The average number of top grossing films over the last few years that are driven by stars has fallen by 200-300 per cent," says Steve Zeitchik of the Hollywood Reporter.

The result is that Harrison Ford has been forced to accept a radical financial arrangement for Indiana Jones and the Crystal Skull, which will be premiered at the Cannes film festival. Paramount Pictures has insisted that the film must take more than $400m at the box office, covering its production and marketing costs and some distribution fees, before Ford, director Steven Spielberg and producer George Lucas, none of whom is receiving an upfront fee, see a cent.

The upside for the three men is that if the film does recoup the $400m, between them they'll get 87.5 cents of every dollar thereafter. "It's good for both parties," says media analyst Harold Vogel. "If the talent has a true belief in the movie, they are taking a little more risk in exchange for a much larger share of the profits."