| APA | HFO. (2012, February 10). In Acronym Geek. Retrieved 17:07, February 10, 2012, from http://www.acronymgeek.com/HFO |
| MLA | "HFO." Acronym Geek. (2012). Acronym Geek. 10 Feb 2012 <http://www.acronymgeek.com/HFO>. |
| MHRA | 'HFO', Acronym Geek, 10 February 2012, <http://www.acronymgeek.com/HFO> [accessed 10 February 2012] |
| Chicago | "HFO", http://www.acronymgeek.com/HFO (accessed February 10, 2012). |
| CBE/CSE | HFO [Internet]. Acronym Geek; 2012 Feb 10 [cited 2012 Feb 10]. Available from: http://www.acronymgeek.com/HFO. |
| Bluebook | HFO, http://www.acronymgeek.com/HFO (last visited February 10, 2012). |
| Bluebook: Harvard JOLT | See Acronym Geek, HFO, http://www.acronymgeek.com/HFO (optional description here) (as of Feb. 10, 2012, 17:07). |
| AMA | HFO. Acronym Geek. February 10, 2012, 17:07. Available at: http://www.acronymgeek.com/HFO. Accessed February 10, 2012, 17:07. |