| APA | OP. (2012, February 14). In Acronym Geek. Retrieved 06:55, February 14, 2012, from http://www.acronymgeek.com/OP |
| MLA | "OP." Acronym Geek. (2012). Acronym Geek. 14 Feb 2012 <http://www.acronymgeek.com/OP>. |
| MHRA | 'OP', Acronym Geek, 14 February 2012, <http://www.acronymgeek.com/OP> [accessed 14 February 2012] |
| Chicago | "OP", http://www.acronymgeek.com/OP (accessed February 14, 2012). |
| CBE/CSE | OP [Internet]. Acronym Geek; 2012 Feb 14 [cited 2012 Feb 14]. Available from: http://www.acronymgeek.com/OP. |
| Bluebook | OP, http://www.acronymgeek.com/OP (last visited February 14, 2012). |
| Bluebook: Harvard JOLT | See Acronym Geek, OP, http://www.acronymgeek.com/OP (optional description here) (as of Feb. 14, 2012, 06:55). |
| AMA | OP. Acronym Geek. February 14, 2012, 06:55. Available at: http://www.acronymgeek.com/OP. Accessed February 14, 2012, 06:55. |