This show is VERY very violent, VERY very often. There is a murder in nearly every single episode, usually by "shanking", or stabbing/cutting with makeshift blades, though in the show prisoners and guards are killed by electrocution (The electric chair is frequently used for execution, though the firing squad and hanging (Prisoners are allowed to chose their means of execution) are used also) and beating and even shooting are used to kill and maim.
Drug trade is very active in the prison and many, many prisoners are killed because of it.
When a prisoner is introduced, there crime is shown (Albeit in slightly muted and in often dulled view) while a narrator tells us their name and prison number. Flashbacks to these (In the same dulled view) sometimes occur.
Rape is very, very common in the prison, and the majority of guards are totally apathetic, if not encouraging, of it.
Blood is shown in almost every violent scene (Gore is never shown).
Insane prisoners do things such as cut their faces up, put their waste on themselves, etc. One even eats himself to death (Only aftermath shown, very bloody, with a totally apathetic guard commenting on how much paperwork it will cause them).
Violent assaults include a guard having his eyes cut out because of his past membership in a gang, another one having their achilles tendon cut because they beat a prisoner basketball team in a tournament, and in a few instances of limb removal. Attempted murders are not uncommon.
Guards frequently abuse, beat and even kill prisoners, though not all do.
This a very brutal, cold, violent show, as it is intended to be: Murders are frequent and usually without remorse. People are stabbed, shot (In flashbacks, and even once in the prison), raped, and overall abused constantly and without letup. Oz is a maximum security prison, and murderers, rapists, and arsonists are mixed with common thieves and white-collar criminals with unpleasant results. Best friends murder each other, naive people are taken advantage of, prisoners use their connections on the street to murder while in prison, and much more happens. This show is not for the squeamish nor people who cannot endure watching constant, systematic violence. Prison is emphasized to be a place where you are turned into a hard-core survivor or killed.