Members of the so-called coloured population are incarcerated at a rate almost double that of their black compatriots, says the SA Institute of Race Relations (SAIRR).
Evidence suggested the higher prison rate could be attributed to the prevalence of gangsterism, alcohol and drug abuse among this group, the institute said in a statement on Tuesday.
"In October 2007, some 80 percent of the South African prison population was made up of Africans, who also made up 79 percent of the entire South African population.
"However, the coloured population was incarcerated at a rate of almost 651 per 100 000 people. This was almost twice the imprisonment rate of the African population, which was 342 per 100 000 people in 2007.
"White and Indian populations were incarcerated at the same rate of around 60 per 100 000 people."
The SAIRR said its analysis of prison populations - published in the 2007/08 edition of its South Africa Survey - was based on figures from the department of correctional services.
"This analysis does not seek to suggest, by any means, that some population groups are more criminally-inclined than others.
"Rather, it seeks to identify peculiar environmental influences that might drive members of some communities towards criminal activity."
Research had shown that some population groups, such as Indians and whites, had a greater proportion of stable families.
Other communities, such as those of the Limpopo region, had better social cohesion than others.
"Furthermore, there was evidence that criminal gang activity and drug and alcohol abuse were more prevalent among communities populated by coloured people than others."
The statement quotes SAIRR researcher Kerwin Lebone as saying South Africa's "infamously low" conviction rates needed to be considered when studying the analysis.
A much higher conviction rate might have resulted in different incarceration rates among the races.
That the prison population itself would stay overwhelmingly African was a function of South Africa's demographics.
"Owing to the relatively greater incomes of the white and Indian populations and their greater levels of education... it might well be the case that they enjoyed a superior standard of legal representation than did the other two population groups, and could thus avoid jail," he said. - Sapa