Police and the ACT Government have offered the money to help provide clues to the murders of Susan Winburn in 2004, Kathryn Grosvenor in 2002 and Irma Palasics in 1999.

A reward of $250,000 is on offer for information leading to arrests in the cases of Ms Grosvenor and Ms Winburn.

The $100,000 reward for information relating to the death of Mrs Palasics has been withdrawn.

A spokesman for Police Minister Simon Corbell said no claims had been made on the rewards in each of the cases. He said despite the lures producing limited results, the Government believed they were an important tool.

''Rewards are not used in all cases but can be an effective resource to encourage members of the community to supply authorities with information about crimes in the more serious categories,'' the spokesman said.

Professor Paul Wilson, of Bond University, said evidence from Australia and throughout the world showed limited success from police offering rewards.

''The chances of a reward eliciting useful information are very small, rewards are a last ditch attempt and have a very low success rate,'' Professor Wilson said.

He said the method was often employed so police and governments could show the public the cases remained high priorities.

Professor Wilson said typically resources were better spent in using cold-case examiners, officers from another jurisdiction or independent forensic psychiatrists to examine the cases.

In recent years, ACT Policing has used the services of cold-case investigator Professor David Barclay from Britain's National Crime and Operations Faculty to examine a number of cases.