| APA | HIO. (2012, February 13). In Acronym Geek. Retrieved 22:54, February 13, 2012, from http://www.acronymgeek.com/HIO |
| MLA | "HIO." Acronym Geek. (2012). Acronym Geek. 13 Feb 2012 <http://www.acronymgeek.com/HIO>. |
| MHRA | 'HIO', Acronym Geek, 13 February 2012, <http://www.acronymgeek.com/HIO> [accessed 13 February 2012] |
| Chicago | "HIO", http://www.acronymgeek.com/HIO (accessed February 13, 2012). |
| CBE/CSE | HIO [Internet]. Acronym Geek; 2012 Feb 13 [cited 2012 Feb 13]. Available from: http://www.acronymgeek.com/HIO. |
| Bluebook | HIO, http://www.acronymgeek.com/HIO (last visited February 13, 2012). |
| Bluebook: Harvard JOLT | See Acronym Geek, HIO, http://www.acronymgeek.com/HIO (optional description here) (as of Feb. 13, 2012, 22:54). |
| AMA | HIO. Acronym Geek. February 13, 2012, 22:54. Available at: http://www.acronymgeek.com/HIO. Accessed February 13, 2012, 22:54. |