| Country | Country name |
| Solomon Islands | conventional long form: none conventional short form: Solomon Islands local long form: none local short form: Solomon Islands former: British Solomon Islands |
| Somalia | conventional long form: none conventional short form: Somalia local long form: Jamhuuriyada Demuqraadiga Soomaaliyeed local short form: Soomaaliya former: Somali Republic, Somali Democratic Republic |
| South Africa | conventional long form: Republic of South Africa conventional short form: South Africa former: Union of South Africa abbreviation: RSA |
| South Georgia and the South Sandwich Islands | conventional long form: South Georgia and the South Sandwich Islands conventional short form: South Georgia and South Sandwich Islands abbreviation: SGSSI |
| South Sudan | conventional long form: Republic of South Sudan conventional short form: South Sudan |
| Southern Ocean | void |
| Spain | conventional long form: Kingdom of Spain conventional short form: Spain local long form: Reino de Espana local short form: Espana |
| Spratly Islands | conventional long form: none conventional short form: Spratly Islands |
| Sri Lanka | conventional long form: Democratic Socialist Republic of Sri Lanka conventional short form: Sri Lanka local long form: Shri Lamka Prajatantrika Samajaya di Janarajaya/Ilankai Jananayaka Choshalichak Kutiyarachu local short form: Shri Lamka/Ilankai former: Serendib, Ceylon |
| Sudan | conventional long form: Republic of the Sudan conventional short form: Sudan local long form: Jumhuriyat as-Sudan local short form: As-Sudan former: Anglo-Egyptian Sudan |
| Suriname | conventional long form: Republic of Suriname conventional short form: Suriname local long form: Republiek Suriname local short form: Suriname former: Netherlands Guiana, Dutch Guiana |
| Svalbard | conventional long form: none conventional short form: Svalbard (sometimes referred to as Spitsbergen) |
| Swaziland | conventional long form: Kingdom of Swaziland conventional short form: Swaziland local long form: Umbuso weSwatini local short form: eSwatini |