| APA | HKO. (2012, February 10). In Acronym Geek. Retrieved 01:51, February 10, 2012, from http://www.acronymgeek.com/HKO |
| MLA | "HKO." Acronym Geek. (2012). Acronym Geek. 10 Feb 2012 <http://www.acronymgeek.com/HKO>. |
| MHRA | 'HKO', Acronym Geek, 10 February 2012, <http://www.acronymgeek.com/HKO> [accessed 10 February 2012] |
| Chicago | "HKO", http://www.acronymgeek.com/HKO (accessed February 10, 2012). |
| CBE/CSE | HKO [Internet]. Acronym Geek; 2012 Feb 10 [cited 2012 Feb 10]. Available from: http://www.acronymgeek.com/HKO. |
| Bluebook | HKO, http://www.acronymgeek.com/HKO (last visited February 10, 2012). |
| Bluebook: Harvard JOLT | See Acronym Geek, HKO, http://www.acronymgeek.com/HKO (optional description here) (as of Feb. 10, 2012, 01:51). |
| AMA | HKO. Acronym Geek. February 10, 2012, 01:51. Available at: http://www.acronymgeek.com/HKO. Accessed February 10, 2012, 01:51. |