| APA | OPON. (2012, February 17). In Acronym Geek. Retrieved 07:27, February 17, 2012, from http://www.acronymgeek.com/OPON |
| MLA | "OPON." Acronym Geek. (2012). Acronym Geek. 17 Feb 2012 <http://www.acronymgeek.com/OPON>. |
| MHRA | 'OPON', Acronym Geek, 17 February 2012, <http://www.acronymgeek.com/OPON> [accessed 17 February 2012] |
| Chicago | "OPON", http://www.acronymgeek.com/OPON (accessed February 17, 2012). |
| CBE/CSE | OPON [Internet]. Acronym Geek; 2012 Feb 17 [cited 2012 Feb 17]. Available from: http://www.acronymgeek.com/OPON. |
| Bluebook | OPON, http://www.acronymgeek.com/OPON (last visited February 17, 2012). |
| Bluebook: Harvard JOLT | See Acronym Geek, OPON, http://www.acronymgeek.com/OPON (optional description here) (as of Feb. 17, 2012, 07:27). |
| AMA | OPON. Acronym Geek. February 17, 2012, 07:27. Available at: http://www.acronymgeek.com/OPON. Accessed February 17, 2012, 07:27. |