| APA | OPX. (2012, February 13). In Acronym Geek. Retrieved 23:19, February 13, 2012, from http://www.acronymgeek.com/OPX |
| MLA | "OPX." Acronym Geek. (2012). Acronym Geek. 13 Feb 2012 <http://www.acronymgeek.com/OPX>. |
| MHRA | 'OPX', Acronym Geek, 13 February 2012, <http://www.acronymgeek.com/OPX> [accessed 13 February 2012] |
| Chicago | "OPX", http://www.acronymgeek.com/OPX (accessed February 13, 2012). |
| CBE/CSE | OPX [Internet]. Acronym Geek; 2012 Feb 13 [cited 2012 Feb 13]. Available from: http://www.acronymgeek.com/OPX. |
| Bluebook | OPX, http://www.acronymgeek.com/OPX (last visited February 13, 2012). |
| Bluebook: Harvard JOLT | See Acronym Geek, OPX, http://www.acronymgeek.com/OPX (optional description here) (as of Feb. 13, 2012, 23:19). |
| AMA | OPX. Acronym Geek. February 13, 2012, 23:19. Available at: http://www.acronymgeek.com/OPX. Accessed February 13, 2012, 23:19. |