Every cinemagoer has an opinion about how a film will perform at the box office. We've seen the trailers, read the reviews, been lambasted by immense marketing campaigns and bought a burger chain tie-in meal.

Now Joe-cinemagoing-public has a chance to put his money where his mouth is and try to profit from the big blockbusters by placing a bet on a film's US opening and first four weeks grosses.

Cantor Index (www.cantorindex.com) has launched an online betting service that allows the public to try its hand at predicting which films will fly and which will flop. "Our customers are continuously looking for new types of bets, whether in the realm of finance, sport, politics or entertainment", says Lee Amaitis, President and CEO of Cantor Fitzgerald International. The Index, which recently acquired the Hollywood Stock Exchange (HSX.com), is starting the betting with Jurassic Park 3 and Tim Burton's Planet Of The Apes which open in the US this week and next respectively.

The bets are based on an initial spread set by Cantor Index. For the latest Jurassic Park installment, for example, you bet whether the film will gross less than $47m or more than $49m this weekend. Therefore if you want to bet it will roar at the US box office then you might put on the minimum £1 a point bet (maximum bet £100 a point), where a point equals $1m at the box office. This means that for every $1m the film grosses above $49m you win £1, but for every $1m it falls below $49m you lose £1. Equally should you believe the monster will keel over and die you can bet against it and for every $1m it takes less than $47m you win your per-point bet.