Home Postcodes by state SA 5166 Postcode 5166 5166 is the postcode for O'Sullivan Beach, SA. Localities with postcode 5166O'Sullivan BeachSA Postcode 5166 State or territory South Australia (SA) Localities 1 Council area Onkaparinga Council area based on Australian Bureau of Statistics data (ASGS Edition 3), CC BY 4.0. Postcode 5165 · Postcode 5167