Sequel and other derivative rights to a film - such as prequel, remake and TV or stage-adaptation rights - generally belong to the studio or production company that makes the film for the entire term of the copyright. Exceptions might occur when a script is written on spec or when the author of an underlying work, such as a novel, grants the production company the right to make just one film.

Derivative rights can become available for acquisition by outside producers when the original production company goes bankrupt or if the company decides not to make a sequel because talent is unavailable. Derivative rights are also put up for sale by library owners who choose not to exploit rights to their library titles themselves.

Currently, suggests Julie Meldal-Johnsen, senior vice-president of business affairs at Granada America - controller of the ITC and Rank libraries - the market for derivative rights is fairly strong as sequels and remakes "have done very well at the box office, especially those in the $30m-$40m range. They're a pre-existing brand, and there's a perception that there's a huge amount of marketing value to be gained from a pre-existing brand."

The rights can be divided up or sold as a package and prices can range from a few hundred thousand dollars to several million. Sometimes sequel or remake rights are sold with a writer or director attached.

Initially, buyers will often acquire a one-year or 18-month option on the rights that can be renewed one or more times. The option fee can then be applied against the outright purchase price, which would be paid by the time principal photography begins.

Sellers will often include a reversion provision in the rights deal, meaning that if the film is not made after a period of up to 10 years the rights revert back to the seller.

Buyers also need to be aware of hidden costs - such as separate payments that may need to be made to secure rights to underlying material, or payments that are due to the original film's writers if and when a sequel is made - and of sequel options that might have been written into the original film's distribution deals.