| APA | CPEN. (2012, February 15). In Acronym Geek. Retrieved 18:02, February 15, 2012, from http://www.acronymgeek.com/CPEN |
| MLA | "CPEN." Acronym Geek. (2012). Acronym Geek. 15 Feb 2012 <http://www.acronymgeek.com/CPEN>. |
| MHRA | 'CPEN', Acronym Geek, 15 February 2012, <http://www.acronymgeek.com/CPEN> [accessed 15 February 2012] |
| Chicago | "CPEN", http://www.acronymgeek.com/CPEN (accessed February 15, 2012). |
| CBE/CSE | CPEN [Internet]. Acronym Geek; 2012 Feb 15 [cited 2012 Feb 15]. Available from: http://www.acronymgeek.com/CPEN. |
| Bluebook | CPEN, http://www.acronymgeek.com/CPEN (last visited February 15, 2012). |
| Bluebook: Harvard JOLT | See Acronym Geek, CPEN, http://www.acronymgeek.com/CPEN (optional description here) (as of Feb. 15, 2012, 18:02). |
| AMA | CPEN. Acronym Geek. February 15, 2012, 18:02. Available at: http://www.acronymgeek.com/CPEN. Accessed February 15, 2012, 18:02. |