| APA | 991. (2012, February 12). In Acronym Geek. Retrieved 06:58, February 12, 2012, from http://www.acronymgeek.com/991 |
| MLA | "991." Acronym Geek. (2012). Acronym Geek. 12 Feb 2012 <http://www.acronymgeek.com/991>. |
| MHRA | '991', Acronym Geek, 12 February 2012, <http://www.acronymgeek.com/991> [accessed 12 February 2012] |
| Chicago | "991", http://www.acronymgeek.com/991 (accessed February 12, 2012). |
| CBE/CSE | 991 [Internet]. Acronym Geek; 2012 Feb 12 [cited 2012 Feb 12]. Available from: http://www.acronymgeek.com/991. |
| Bluebook | 991, http://www.acronymgeek.com/991 (last visited February 12, 2012). |
| Bluebook: Harvard JOLT | See Acronym Geek, 991, http://www.acronymgeek.com/991 (optional description here) (as of Feb. 12, 2012, 06:58). |
| AMA | 991. Acronym Geek. February 12, 2012, 06:58. Available at: http://www.acronymgeek.com/991. Accessed February 12, 2012, 06:58. |