Jeremy Brabrooke, 56, was last seen at Ford Prison in West Sussex on Wednesday, November 14.
A police spokesperson said officers are 'keen to locate and detain the 56-year-old'.
Brabrooke was sentenced to life imprisonment in 1988 for murder in Bradford, West Yorkshire, and is known to have links to Hayling Island and Portsmouth in Hampshire, police said.
Anyone who sees him or knows where he may be is asked to call 999.
According to the Ministry of Justice website, HMP Ford is a Category D establishment with an 'emphasis on resettlement'.
Formerly a fleet air arm station, it converted to an open prison in 1960, the website said.
An open prison has the minimum restriction on inmates' movements and activities.
You can also contact the independent charity Crimestoppers anonymously on 0800 555 111 or report it online.