| APA | HIOP. (2012, February 15). In Acronym Geek. Retrieved 15:00, February 15, 2012, from http://www.acronymgeek.com/HIOP |
| MLA | "HIOP." Acronym Geek. (2012). Acronym Geek. 15 Feb 2012 <http://www.acronymgeek.com/HIOP>. |
| MHRA | 'HIOP', Acronym Geek, 15 February 2012, <http://www.acronymgeek.com/HIOP> [accessed 15 February 2012] |
| Chicago | "HIOP", http://www.acronymgeek.com/HIOP (accessed February 15, 2012). |
| CBE/CSE | HIOP [Internet]. Acronym Geek; 2012 Feb 15 [cited 2012 Feb 15]. Available from: http://www.acronymgeek.com/HIOP. |
| Bluebook | HIOP, http://www.acronymgeek.com/HIOP (last visited February 15, 2012). |
| Bluebook: Harvard JOLT | See Acronym Geek, HIOP, http://www.acronymgeek.com/HIOP (optional description here) (as of Feb. 15, 2012, 15:00). |
| AMA | HIOP. Acronym Geek. February 15, 2012, 15:00. Available at: http://www.acronymgeek.com/HIOP. Accessed February 15, 2012, 15:00. |