| APA | HEI. (2012, February 15). In Acronym Geek. Retrieved 03:27, February 15, 2012, from http://www.acronymgeek.com/HEI |
| MLA | "HEI." Acronym Geek. (2012). Acronym Geek. 15 Feb 2012 <http://www.acronymgeek.com/HEI>. |
| MHRA | 'HEI', Acronym Geek, 15 February 2012, <http://www.acronymgeek.com/HEI> [accessed 15 February 2012] |
| Chicago | "HEI", http://www.acronymgeek.com/HEI (accessed February 15, 2012). |
| CBE/CSE | HEI [Internet]. Acronym Geek; 2012 Feb 15 [cited 2012 Feb 15]. Available from: http://www.acronymgeek.com/HEI. |
| Bluebook | HEI, http://www.acronymgeek.com/HEI (last visited February 15, 2012). |
| Bluebook: Harvard JOLT | See Acronym Geek, HEI, http://www.acronymgeek.com/HEI (optional description here) (as of Feb. 15, 2012, 03:27). |
| AMA | HEI. Acronym Geek. February 15, 2012, 03:27. Available at: http://www.acronymgeek.com/HEI. Accessed February 15, 2012, 03:27. |