| Abbreviation | Definition |
|---|---|
| OCA | Orthodox Church in America |
| OCE | Office of Church Engagement |
| OCEC | Oregon City Evangelical Church |
| OCMC | Oxford Circle Mennonite Church |
| OCMN | Ohio Church Multiplication Network |
| OCPC | Old Cutler Presbyterian Church |
| OCUC | Ottawa Chinese United Church |
| ODBC | Open Door Bible Church |
| ODCC | Oakland Drive Christian Church |
| ODPC | Ocean Drive Presbyterian Church |
| ODPC | Open Door Presbyterian Church |
| OECTA | Ontario English Catholic Teachers Association |
| OEPC | Oreland Evangelical Presbyterian Church |
| OFBC | Old Fort Baptist Church |
| OFBC | Olmsted Falls Baptist Church |
| OFLC | Our Father Lutheran Church |
| OHC | Oak Hills Church |
| OHCC | Oakland Hills Community Church |
| OHCC | Oracle House Christian Church |
| OHCT | Oxfordshire Historic Churches Trust |