| OAK Oakridge International Limited | Healthcare | $2.2M |
| OB1 Orbminco Limited | Basic Materials | $3.5M |
| OBL Omni Bridgeway Limited | Financial Services | $477.9M |
| OBM Ora Banda Mining Limited | Basic Materials | $2.50B |
| OCA Oceania Healthcare Limited | Healthcare | $441.8M |
| OCC Orthocell Limited | Healthcare | $169.9M |
| OCL Objective Corporation Limited | Technology | $979.1M |
| OCN Oceana Lithium Limited | Basic Materials | $101.2M |
| OCT Octava Minerals Limited | Basic Materials | $2.1M |
| OD6 OD6 Metals Limited | Basic Materials | $16.0M |
| ODA Orcoda Limited | Industrials | $8.1M |
| ODE Odessa Minerals Limited | Basic Materials | $35.3M |
| ODY Odyssey Gold Limited | Basic Materials | $34.8M |
| OEC Orbital Corporation Limited | Industrials | $26.4M |
| OEL Otto Energy Limited | Energy | $24.0M |
| OFX OFX Group Limited | Financial Services | $133.8M |
| OIL Optiscan Imaging Limited | Technology | $130.5M |
| OLI Oliver's Real Food Limited | Consumer Cyclical | $3.2M |
| OLL OpenLearning Limited | Technology | $7.0M |
| OLY Olympio Metals Limited | Basic Materials | $4.6M |
| OM1 Omnia Metals Group Ltd | Basic Materials | $3.9M |
| OMA Omega Oil & Gas Limited | Energy | $222.4M |
| OMG Omg Group Fpo [omg] | Consumer Defensive | $6.6M |
| OMH OM Holdings Limited | Basic Materials | $168.2M |
| OML oOh!media Limited | Communication Services | $768.5M |
| OMX Orange Minerals NL | Basic Materials | $9.0M |
| ONE Oneview Healthcare PLC | Healthcare | $146.9M |
| OOO BetaShares - Crude Oil Index Currency Hedged Complex ETF | ETF | $81.7M |
| OPH Ophir Asset Management Pty Ltd - Ophir High Conviction Fund | Fund | $621.0M |
| OR3 Oreresourc Fpo [or3] | Basic Materials | $65.4M |
| ORA Orora Limited | Consumer Cyclical | $1.70B |
| ORD Ordell Minerals Limited | Basic Materials | $32.8M |
| ORE Orezone Gold Corporation | Basic Materials | $1.38B |
| ORG Origin Energy Limited | Energy | $18.57B |
| ORI Orica Limited | Basic Materials | $10.59B |
| ORN Orion Minerals Limited | Basic Materials | $223.9M |
| ORP Orpheus Uranium Limited | Basic Materials | $22.8M |
| OSL OncoSil Medical Limited | Healthcare | $12.0M |
| OSM Osmond Resources Limited | Basic Materials | $77.3M |
| OSX Osteopore Limited | Healthcare | $1.3M |
| OVT Ovanti Ltd | Technology | $3.4M |
| OZF State Street SPDR S&P/ASX 200 Financials EX A-REIT ETF | ETF | $45.0M |
| OZM OzAurum Resources Limited | Basic Materials | $16.8M |
| OZR State Street SPDR S&P/ASX 200 Resources ETF | ETF | $255.5M |
