Many prisoners serve sentences of just a few weeks
A former prison governor has called for jail sentences of less than six months to be scrapped.
Professor Alec Spencer, who has run Saughton, Peterhead and Glenochil prisons, said short sentences were an expensive waste of time.
A total of 8,603 prisoners served sentences under six months in Scotland last year.
Prof Spencer said short sentences did not give prison staff enough time to address the causes of criminality.
He told BBC Radio Scotland's Newsdrive programme: "In the last year there were 8,603 people in for under six months - on average they served 24.2 days.
"The problem with that is that you can't do a lot with people. If they have got addiction problems you can't deal with those, or if they have got some need they can't start addressing them in that very short period of time.
"What evidence tells us is that prison doesn't work for short sentences. For long-term prisoners who are dangerous to the public it is absolutely the right place for them, but for very short sentences there is absolutely no point and it does not reduce crime."
He said that many people sent to prison for short sentences lost their employment and accommodation, leaving them homeless and unemployed and more of a burden on the state.
And he dismissed claims that persistent petty offenders often needed a "short, sharp shock".
"All the evidence points to the fact that if you throw them into prison they are still going to come out and offend. All it does is add to the cost and create a whole lot of extra problems," he said.
"If somebody has got an addiction problem and they are going stealing in shops, sending them to prison is not going to solve that. They need to go onto an addiction programme, which are to be found in the community.
"I realise also that there is a shortage of them, but what we need to do is to make sure that there is money available for these services.
"You can't do that if you are spending millions and millions on sending people to prison."
Prof Spencer said there were about 500 or 600 people at any one time serving very short sentences, costing the country about £20m a year.