Last month the double-amputee runner was found guilty of culpable homicide, or negligent killing.
Sentences for such a crime can range from a suspended sentence and a fine to as many as 15 years in prison.
Oscar Pistorius arrives in court on Monday morning
Pistorius, once a celebrated athlete who ran in the 2012 Olympics, was charged with premeditated murder in a televised trial that transfixed many people around the world, but judge Thokozile Masipa found him not guilty of that charge.
She drew criticism from some South Africans who thought Pistorius could at least have been convicted of a lesser murder charge on the grounds that he knew a person could die when he fired four bullets through a toilet door in his home early on Valentine's Day last year.
Steenkamp, a 29-year-old model, died in the hail of bullets, and prosecutors said Pistorius had opened fire in anger after the couple argued. The runner testified that he mistook Steenkamp for an intruder who was about to come out of the toilet and attack him.
Pistorius and Steenkamp in November 2012, three months before her death
South African lawyers vary widely in predictions about what kind of sentence Pistorius will get.
Some say he is unlikely to go to jail because defence lawyers will successfully argue that the athlete is a first-time offender with a disability that would subject him to particular hardship in prison, while others anticipate that Pistorius will be sentenced to some prison time because of the severity of his crime.
"I think that the probabilities are that the judge will send him to prison for a certain period, but not a very long one," said George Bizos, a human rights lawyer. He did not specify the length of a possible jail term.
There are "clear aggravating and mitigating factors" that could influence the judge's decision-making but that it was difficult to accurately predict the penalty because the "sentencing law is so individually applied," said Kelly Phelps, a senior lecturer in the public law department at the University of Cape Town.