| APA | OPVO. (2012, February 15). In Acronym Geek. Retrieved 17:38, February 15, 2012, from http://www.acronymgeek.com/OPVO |
| MLA | "OPVO." Acronym Geek. (2012). Acronym Geek. 15 Feb 2012 <http://www.acronymgeek.com/OPVO>. |
| MHRA | 'OPVO', Acronym Geek, 15 February 2012, <http://www.acronymgeek.com/OPVO> [accessed 15 February 2012] |
| Chicago | "OPVO", http://www.acronymgeek.com/OPVO (accessed February 15, 2012). |
| CBE/CSE | OPVO [Internet]. Acronym Geek; 2012 Feb 15 [cited 2012 Feb 15]. Available from: http://www.acronymgeek.com/OPVO. |
| Bluebook | OPVO, http://www.acronymgeek.com/OPVO (last visited February 15, 2012). |
| Bluebook: Harvard JOLT | See Acronym Geek, OPVO, http://www.acronymgeek.com/OPVO (optional description here) (as of Feb. 15, 2012, 17:38). |
| AMA | OPVO. Acronym Geek. February 15, 2012, 17:38. Available at: http://www.acronymgeek.com/OPVO. Accessed February 15, 2012, 17:38. |