| APA | NPEN. (2012, February 15). In Acronym Geek. Retrieved 13:07, February 15, 2012, from http://www.acronymgeek.com/NPEN |
| MLA | "NPEN." Acronym Geek. (2012). Acronym Geek. 15 Feb 2012 <http://www.acronymgeek.com/NPEN>. |
| MHRA | 'NPEN', Acronym Geek, 15 February 2012, <http://www.acronymgeek.com/NPEN> [accessed 15 February 2012] |
| Chicago | "NPEN", http://www.acronymgeek.com/NPEN (accessed February 15, 2012). |
| CBE/CSE | NPEN [Internet]. Acronym Geek; 2012 Feb 15 [cited 2012 Feb 15]. Available from: http://www.acronymgeek.com/NPEN. |
| Bluebook | NPEN, http://www.acronymgeek.com/NPEN (last visited February 15, 2012). |
| Bluebook: Harvard JOLT | See Acronym Geek, NPEN, http://www.acronymgeek.com/NPEN (optional description here) (as of Feb. 15, 2012, 13:07). |
| AMA | NPEN. Acronym Geek. February 15, 2012, 13:07. Available at: http://www.acronymgeek.com/NPEN. Accessed February 15, 2012, 13:07. |