Some cast members that played prisoners have noted that, throughout the series, if you showed up late to the set, your punishment would be that your character would either die or be raped the next week.
Throughout the series, Kareem Said, Timmy Kirk, James Robson and Jeremiah Cloutier are the only inmates & Father Ray Mukada and Sister Peter Marie are the only staff to pronounce Vern Schillinger's last name correctly. Alva Case in season 2 also pronounces it correctly.
The prisoner's inmate numbers begin with two digits indicating the year they were incarcerated and then a letter which is the first letter of their last name. The only exception is inmates whose last name begins with O, such as Ryan O'Reilly. Because prison officials believed that an O could be easily mistaken for a zero, they use the letter P for inmates whose last name begins with O.
Chuck Zito (Pancamo) first auditioned as a Biker, having being a veteran member of the Hell's Angels Biker Club. However because of his complexion and heavy New York accent, Tom Fontana thought he'd fit in better with the Italians on the series.
Prior to the boxing scenes in season 3, series creator Tom Fontana asked the actors involved if they had experience boxing. All said yes, but it turned out that only Chuck Zito had ever done any actual boxing.
Dean Winters (Ryan O'Reilly) and J.K. Simmons (Schillinger) both went on to be featured in insurance commercials: Winters as "Mayhem" the Allstate spokesman, and Simmons as the Farmers Insurance Professor.
In the 2013 book "Difficult Men: Behind the Scenes of a Creative Revolution: From The Sopranos and The Wire to Mad Men and Breaking Bad", author Brett Martin notes that while he was a writer and executive producer on Oz, Tom Fontana would often subsidize Oz actors' outside theater projects. Fontana said that he gave the donations so that he wouldn't actually have to attend the shows--that it was "worth $1000 not to have to see a play."
In contrast to many screen depictions of prison (such as The Shawshank Redemption (1994)), none of the characters imprisoned in Oz are innocent of their crimes. Even Jason Kramer, whose conviction is overturned due to police misconduct is heavily implied to be guilty of the crime he was sent to prison for. Series creator Tom Fontana has said that this decision to only have guilty characters was a deliberate one in order to better highlight the series themes of redemption
According to Tom Fontana, Dean Winters had a crush on Luna Lauren Velez and requested a sex scene to be filmed with their characters. A scene in which O'Reily fantasizes about having sex with Nathan was filmed much to Winters' delight.
Donald Groves, the prisoner that kills his mother and father and eats their flesh, is played by the late Sean Whitesell. In addition to appearing in the first season, he also wrote two episodes for the fifth season. Those episodes were "Laws of Gravity" and "Dream and Little Dream For Me". He sadly passed away from cancer in 2015.
Game Of Thrones actor, Peter Dinklage (A.K.A Tyrion Lannister in G.O.T), plays an unnamed murder victim, who is thrown off a rooftop by one of the characters, during an "Augustus Hill" introduction of that character.
Although Oz was created to depict what prison life was actually life for prisoners, many fans and the few cast members who had done real time in prison stated it was nothing like the series. In contrast, quite the opposite as mostly all U.S. Prisons keep inmates segregated and locked in their cells for most of the time. In the sense that this was a series; having characters and an intricate storyline, it was obvious the show be given more "fluff" to appeal to its viewers.
Even though it is never stated where the show takes place, it is hinted to be around the Buffalo, NY area. A Buffalo Bills helmet is seen in Glynn's office and Officer Diane Whittlesey mentions a "Chevy plant" (possibly referencing GM's Tonawanda plant in Buffalo). Also, series creator, Tom Fontana's hometown is Buffalo. Tim McManus tells a story to Kareem Said about the Attica prison riots during the season 1 finale. Attica, NY is fairly close to Buffalo. Maybe referencing that McManus is close to home. Most of the flashbacks that show what landed certain characters in Oz take place in New York City, proven by the look of the environment and during the flashback of Chris Keller, you see an actual NYC squad car behind the generic squad car that is pursuing Keller on a bike chase. Meaning that Oz could be a state prison located on the other end of the state from NYC. And last but not least, some believe that Oz is a reference to Attica prison Prison Chief, Russell Oswald. Ironically, even with all the little hints about New York State in the show, the state flag of Delaware is in the lobby of Oz. Thus, throwing the viewer off of an exact location of Oz.
The trivia items below may give away important plot points.
Christopher Meloni (Keller) left the show towards the end of the fourth season because he was also working on Law & Order: Special Victims Unit (1999) and he felt that he could no longer do both shows at the same time. On the show, it was explained that Keller was transferred to another prison. But Meloni missed Oz and decided to return. He decided that being able to work on two great shows simultaneously was worth the physical and emotional toll.
In the first part of the fourth season it was explained that Officer Diane Wittlesey (Edie Falco) moved away to London, GB. In real life, Falco left the show to star in the London production of the play "Side Man". She then went on to play Carmela Soprano in The Sopranos (1999), another HBO production.
Five prisoners are executed throughout the show's run and almost all with different methods: Jefferson Keane and Richard L'Italien die by lethal injection in Season 1; Donald Groves was executed by Firing Squad in Season 1; Shirley Bellinger is executed by hanging in Season 4; and Cyril O'Reilly dies in the electric chair in the series finale.
Kirk Acevedo (Alvarez) was absent from most of the first half of the fourth season because he was working on Band of Brothers (2001). On the show, it was explained that Alvarez had escaped. Acevedo returned for the second half of the fourth season. But shortly after production began on the second half, he landed a recurring role on Third Watch (1999) and had to leave again. This time, it was explained that Alvarez had been put in solitary confinement. In some episodes, archive footage of Acevedo from past episodes was reused.
With the exception of Jason Cramer and Jackson Vahue, none of the inmates who survived until the end of the series ever made it out of Oz. The ones who were paroled, Beecher and Poet, returned to the prison shortly after they were released. The two who escaped, Alvarez and Busmalis, were eventually recaptured.
Jefferson Keane is executed halfway through the first season because the actor portraying him, Leon, refused to commit to a series. When Leon asked Tom Fontana why he was being killed off, Fontana told him it was because he said he wouldn't commit to more than four episodes. Leon replied that he thought he'd been talked out of that and actually wanted to stay.
The prison set was actually an old warehouse that Tom Fontana had revamped. Fontana was also able to move his production offices into the space. Fontana would renew the lease on the space one year at a time in case the show got cancelled. During production on the fourth season, Tom Fontana learned that the owner of the property signed off a 10-year lease to NY1, a local New York City news station. The fourth season finale was titled "Famous Last Words" and ends with a fiery explosion in the prison. This was so that the episode could also serve as the series finale in case Fontana was unable to find a new filming location for the show. Fortunately, Fontana found a similar looking warehouse in New Jersey he could use and the show was able to continue.
By the time of the fourth season finale, they didn't know whether they would be renewed and so Tom Fontana wrote two endings: one where Beecher got paroled and one where he didn't. If the show was canceled they would end on the happy note of Beecher being paroled. The show was renewed but Fontana liked the sequence of Beecher's parole so much that he used it as a sequence in the final season.
J.K. Simmons' spouse Michelle Schumacher made guest appearances as Norma Clark. Their characters don't interact in any way, but Vern notes that Norma's letter is "stinking with cheap perfume" during a mail delivery scene.
Inmates are never seen outdoors - in the prison yard - and thus are seemingly never exposed to sunlight during their time in Oz. Only scenes in which viewers see prisoners having daily exercise are indoors. One exception to this is a scene where Alvarez is shown roaming the streets dark in the night.
In the third season, the medical ward was privatized and taken over by a company called The Weigart Corporation. The Weigart Corporation is also the name of the company that bought St. Eligius Hospital in St. Elsewhere (1982). Series creator Tom Fontana was a writer on St. Elsewhere.