While diamonds are forever, Bond actors tend to lose their shine after the fourth appearance, according to research by a university economist.
Mark Baimbridge, a lecturer at Bradford University, analysed all 17 James Bond films, excluding Goldeneye, to work out what makes for a successful movie. He discovered that even the appeal of Sean Connery, the most popular 007 in terms of box-office admissions, was wearing thin by film number four.
Mr Baimbridge said he chose the Bond oeuvre because it was the best example of a long-running cinema series. "The challenge is to learn what makes a good film and how to avoid turkeys," he said. "Somewhere down the line, the Bond films must have got the recipe right."
While only one feature film in ten can expect to make a profit, every Bond title has made money. Mr Baimbridge measured the success of each film by rental income and cinema admissions in the United States. He analysed how these were affected by ticket price, leading actor, reception by the critics and timing of the film's release.
While it did not seem to matter how much time had elapsed between Bond film's - or even whether they were made before or after the cold war - ticket price did make a difference.
The films also proved more of a box-office hit if they had received Oscar nominations.
Choice of actor was crucial. Connery came out on top, followed by George Lazenby, Roger Moore and then Timothy Dalton.
But Lazenby's popularity could have been affected by the fact he only made one film and therefore had no time to experience the usual waning of audience interest.
"The cut-throat way of looking at this is that film-makers should get rid of their actor after the fourth film and get someone else in to rejuvenate the product," said Mr Baimbridge.
The news is likely to leave Pierce Brosnan, still only on his second film, shaken but not stirred.