It says that overcrowding has been slowly declining in European prisons since 2011, although it remains a problem in one in four prison administrations.
According to the 2014 Council of Europe annual penal statistics (SPACE), the ratio of prisoners fell from 99 inmates for every 100 places in 2011 to 96 inmates per 100 places in 2013, and then to 94 in 2014.
The prison population rate also decreased by seven per cent in 2014 compared to the previous year, from 134 to 124 inmates per 100,000 inhabitants. European prisons remained however close to the top of their capacity, holding 1,600,324 people.
The number of prison administrations suffering from overcrowding decreased significantly (down to 13 in 2014 from 21 in 2013).
The countries with the most crowded penal institutions were Hungary, Belgium, the former Yugoslav Republic of Macedonia, Greece, Albania, Italy, Spain (state administration), Slovenia, France, Portugal, Serbia, Romania and Austria (*).
The survey was conducted for the Council of Europe by the School of Criminal Sciences of the University of Lausanne.
It contains information from 50 out of 52 prison administrations in the 47 Council of Europe member states.
Responding to the findings, Council of Europe Secretary General Thorbjørn Jagland said: "Overcrowding creates enormous obstacles to rehabilitating offenders and thus to better protecting society from crime. It can also breach human rights. I welcome the progress achieved in reducing prison overcrowding. States still affected should do more to eradicate it, including applying alternative measures to imprisonment".
During 2014 there were 1,212,479 individuals under the supervision of agencies in charge of alternative measures to imprisonment such as probation, community services, curfew orders or electronic monitoring in the 45 countries that provided this kind of information for the survey.
Only 6.7 per cent of them were awaiting trial, which shows that non-custodial measures are still seldom used instead of pre-trial detention.
During the year 1,373,912 persons entered into the supervision of these agencies and 1,134,567 left that supervision.
In 2014 foreign inmates represented an average of 21.7 per cent of the total prison population. 34.6 per cent of them were citizens from EU countries. In most central and eastern European countries, the proportion of foreign inmates did not exceed 10 per cent. In southern and western Europe foreigners were over represented in comparison with the total population, their percentage ranging from 25 per cent to 96 per cent of the prison population.
The length of very short custodial sentences slightly decreased in 2013: on average 16 per cent of inmates were serving less than one year sentences, in contrast with 17 per cent in 2012. On the other hand the average proportion of inmates serving sentences of more than 10 years grew from 11.2 per cent to 14.3 per cent.
Drug offences remained the crime for which most offenders were held in custody (16.5 per cent), followed by theft (14 per cent), robbery (13.1 per cent) and homicide (12.3 per cent).
The average amount spent per inmate per day in 2013 was €99, which is higher than in 2012 (€97), although the figures varied greatly across Europe.
In 2013, the 45 prison administrations that provided this data for the survey spent more than €27bn.