| APA | OPP. (2012, February 4). In Acronym Geek. Retrieved 11:05, February 4, 2012, from http://www.acronymgeek.com/OPP |
| MLA | "OPP." Acronym Geek. (2012). Acronym Geek. 4 Feb 2012 <http://www.acronymgeek.com/OPP>. |
| MHRA | 'OPP', Acronym Geek, 4 February 2012, <http://www.acronymgeek.com/OPP> [accessed 4 February 2012] |
| Chicago | "OPP", http://www.acronymgeek.com/OPP (accessed February 4, 2012). |
| CBE/CSE | OPP [Internet]. Acronym Geek; 2012 Feb 4 [cited 2012 Feb 4]. Available from: http://www.acronymgeek.com/OPP. |
| Bluebook | OPP, http://www.acronymgeek.com/OPP (last visited February 4, 2012). |
| Bluebook: Harvard JOLT | See Acronym Geek, OPP, http://www.acronymgeek.com/OPP (optional description here) (as of Feb. 4, 2012, 11:05). |
| AMA | OPP. Acronym Geek. February 4, 2012, 11:05. Available at: http://www.acronymgeek.com/OPP. Accessed February 4, 2012, 11:05. |