* UNANIMOUS OR SPLIT DECISIONS

Like in any appeal court, the decision of the judges could be unanimous or it could be split. The majority decision will stand, which, in this case, would be a 4-3 split.

* MULTIPLE REASONS

If all the judges reach the same decision for the same reasons, it's possible they'll hand down their decision in a single judgment.

If there is a split decision, then there'll be a majority judgment handed down. The decisions of the judges in the minority are called dissents.

Sometimes judges come to the same decision but for different reasons so they'll each publish their own reasons. That means there could be up to seven different opinions handed down.

* SPECIAL LEAVE APPLICATION REFUSED

The High Court has to grant Pell special leave to appeal before they can formally consider the appeal.

Usually this happens before the appeal hearing, but in Pell's case it was decided they'd hear the appeal arguments before making a decision on granting special leave.

If special leave is refused, Pell's conviction will stand and he will remain behind bars.

* SPECIAL LEAVE APPLICATION GRANTED

If the High Court determines there is a legal question for them to consider, then they'll grant special leave.

After that, there's a few paths they can follow:

* APPEAL REFUSED, CONVICTIONS UPHELD

After considering the two days of arguments and written submissions, the High Court justices could determine that there was no error in the Court of Appeal's majority decision to uphold Pell's conviction.

Alternatively they might find that there was an error but not one that affected the ultimate decision.

If either are the case, the appeal will be refused and Pell's convictions will be upheld. He will remain in prison.

* APPEAL BOTH REFUSED AND GRANTED

Because Pell was convicted of charges relating to two separate incidents, it's possible the High Court could grant the appeal in relation to one incident but refuse it in relation to the other.

For example, they might find there wasn't sufficient evidence for a jury to reach a guilty verdict in relation to the second incident, but there was in relation to the first.

That could see Pell's conviction quashed on some charges but not others, meaning he would have to be re-sentenced.

* APPEAL GRANTED, CONVICTION QUASHED

If the High Court determines there was an error in the Court of Appeal majority's decision, they might find that the error was so significant that Pell's convictions should be quashed and he be acquitted.

This would result in his immediate release from prison. This is what his defence want.

* APPEAL GRANTED, PREVIOUS APPEAL TO BE RE-HEARD

Another potential outcome is that the High Court determines there was an error in the Court of Appeal's decision, but it was not one that immediately requires Pell's conviction to be overturned.

It could be ordered that the original appeal be reconsidered, either by the High Court or the Court of Appeal.

Australian Associated Press