The conductors, a woman and two men, sustained minor injuries after the assailant stabbed them during a routine ticket check.
The attacker, who was in Norway illegally, was not carrying identification at the time, newspaper Aftenposten reports.
Unable to produce a ticket, he and a friend – a 46-year-old Norwegian citizen of Chilean origin – tried to force their way off the tram when it stopped at Solli Plass.
The 38-year-old pleaded guilty in court, but claimed he had only gone on the attack after the conductors grabbed his throat, making it difficult for him to breathe. No witnesses verified this version of events.
He also said he had only intended to scare the conductors but ended up stabbing them by accident.
Unconvinced, Oslo district court sentenced him to prison and ordered him to pay 90,000 kroner ($15,000) in damages.