The Old Petrians Alumni Society (OPAS) was started on 4 June 2008. It is a society for all past pupils who attended St Peter's College. OPAS has an identity synonymous with excellence and aims to passionately enable, enhance and sustain the personal and professional relationships built at St Peter's College. The Tak Hiemstra Pavilion is home to the Old Petrians.
Old Pets annual events include:
- Old Pets 5-a-side soccer vs 1st team
- 7-a-side rugby
- 10-year reunions
- Supporting our current student body with presentations, talks and at sporting and cultural events
- Old Petrians