| APA | SO4. (2012, February 11). In Acronym Geek. Retrieved 23:20, February 11, 2012, from http://www.acronymgeek.com/SO4 |
| MLA | "SO4." Acronym Geek. (2012). Acronym Geek. 11 Feb 2012 <http://www.acronymgeek.com/SO4>. |
| MHRA | 'SO4', Acronym Geek, 11 February 2012, <http://www.acronymgeek.com/SO4> [accessed 11 February 2012] |
| Chicago | "SO4", http://www.acronymgeek.com/SO4 (accessed February 11, 2012). |
| CBE/CSE | SO4 [Internet]. Acronym Geek; 2012 Feb 11 [cited 2012 Feb 11]. Available from: http://www.acronymgeek.com/SO4. |
| Bluebook | SO4, http://www.acronymgeek.com/SO4 (last visited February 11, 2012). |
| Bluebook: Harvard JOLT | See Acronym Geek, SO4, http://www.acronymgeek.com/SO4 (optional description here) (as of Feb. 11, 2012, 23:20). |
| AMA | SO4. Acronym Geek. February 11, 2012, 23:20. Available at: http://www.acronymgeek.com/SO4. Accessed February 11, 2012, 23:20. |