| APA | OPEH. (2012, February 15). In Acronym Geek. Retrieved 19:20, February 15, 2012, from http://www.acronymgeek.com/OPEH |
| MLA | "OPEH." Acronym Geek. (2012). Acronym Geek. 15 Feb 2012 <http://www.acronymgeek.com/OPEH>. |
| MHRA | 'OPEH', Acronym Geek, 15 February 2012, <http://www.acronymgeek.com/OPEH> [accessed 15 February 2012] |
| Chicago | "OPEH", http://www.acronymgeek.com/OPEH (accessed February 15, 2012). |
| CBE/CSE | OPEH [Internet]. Acronym Geek; 2012 Feb 15 [cited 2012 Feb 15]. Available from: http://www.acronymgeek.com/OPEH. |
| Bluebook | OPEH, http://www.acronymgeek.com/OPEH (last visited February 15, 2012). |
| Bluebook: Harvard JOLT | See Acronym Geek, OPEH, http://www.acronymgeek.com/OPEH (optional description here) (as of Feb. 15, 2012, 19:20). |
| AMA | OPEH. Acronym Geek. February 15, 2012, 19:20. Available at: http://www.acronymgeek.com/OPEH. Accessed February 15, 2012, 19:20. |