| APA | OPOR. (2012, February 15). In Acronym Geek. Retrieved 13:34, February 15, 2012, from http://www.acronymgeek.com/OPOR |
| MLA | "OPOR." Acronym Geek. (2012). Acronym Geek. 15 Feb 2012 <http://www.acronymgeek.com/OPOR>. |
| MHRA | 'OPOR', Acronym Geek, 15 February 2012, <http://www.acronymgeek.com/OPOR> [accessed 15 February 2012] |
| Chicago | "OPOR", http://www.acronymgeek.com/OPOR (accessed February 15, 2012). |
| CBE/CSE | OPOR [Internet]. Acronym Geek; 2012 Feb 15 [cited 2012 Feb 15]. Available from: http://www.acronymgeek.com/OPOR. |
| Bluebook | OPOR, http://www.acronymgeek.com/OPOR (last visited February 15, 2012). |
| Bluebook: Harvard JOLT | See Acronym Geek, OPOR, http://www.acronymgeek.com/OPOR (optional description here) (as of Feb. 15, 2012, 13:34). |
| AMA | OPOR. Acronym Geek. February 15, 2012, 13:34. Available at: http://www.acronymgeek.com/OPOR. Accessed February 15, 2012, 13:34. |