Gary Rootham absconded from HMP Leyhill on Friday.
The 42-year-old was last seen by prison staff shortly before 5pm.
He was wearing a dark Nike polo shirt, dark jogging bottoms and black trainers with white soles.
Police are warning people not to approach him but to call 999.
Rootham, who is described as being around 5ft 11ins, has short dark brown hair and is usually clean shaven, was serving sentences for matters including driving, robbery and burglary offences.
He has links to Reading and Cornwall.
It comes a day after police in London launched a manhunt for an inmate at HMP Wormwood Scrubs who went on the run after being moved to hospital.
Graham Gomm, 63, was arrested and returned to jail this morning.
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