text: Incarceration rates Gang members account for a rapidly increasing proportion of incarcerations in New Zealand. A New Zealand Ministry of Justice study showed that in 1991 just under 80% of prison inmates had no gang history, and just over 90% had no current gang membership. Of the prison population, 4% were members of the Mongrel Mob and 4.3% former members, while 3.6% were current and 3.2% former members of Black Power. No other gang had more than one percent of the prison population. A similar study in 2003 showed that 11.3% of prison inmates were gang members. Of these, 35% were Mongrel Mob and 33% Black Power, with no other individual gang having more than 5% of the imprisoned gang population. As of April 2013, gang members and affiliates account for over 30% of inmates, with over 10% of New Zealand prisoners being Mongrel Mob members.
  Gang membership
  According to the 2007 book Gangs by English journalist Ross Kemp, New Zealand had more gangs per head than any other country in the world, with about seventy major gangs and over 4,000 patched members in a population of 4 million people. In 2019 the Police recorded 6,500 patched or prospective gang members in the country, with the ten main gangs being the Head Hunters, Bandidos, Hells Angels, King Cobras, Black Power, Mongrel Mob, Tribesmen, Rebels, Devils Henchmen and Highway 61.
  In October 2019, Stuff reported that New Zealand gangs seemed to be recruiting members at a greater rate than the New Zealand Police. Between October 2017 and October 2019, the number of patched gang members and "prospects" had risen by 1,400 to an estimated total of 6,375. By comparison, the number of Police officers during that same period had increased by only 893. Stuff attributed the increase in gang membership to the return of deported "bikie gang" members from Australia, who had been deported under recent Australian anti-bikie gang legislation. In addition, the Mongrel Mob started a female chapter.