| Second Institute of Oceanography | Academic & Science |
| Students Islamic Organization of India | Academic & Science |
| Student Information Online | Academic & Science |
| Studentsamskipnaden i Oslo | Academic & Science |
| Students Islamic Organisation | Academic & Science |
| Students Islamic Organization | Academic & Science |
| Science Institute Of | Academic & Science |
| Skidaway Institute of Oceanography | Academic & Science |
| Scripps Institution of Oceanography | Academic & Science |
| Students Islamic Organisation of India | Academic & Science |
| Surety Information Office | Accounts and Finance |
| Smithton | Airport Code |
| Seller Initiated Offer | Business |
| Social Insurance Organization | Business |
| Silicon Oxide | Chemistry |
| Social Investment Organization | Community |
| Scientific or Industrial Organization (ITU member) | Computer and Networking |
| Spit It Out | Computing |
| System Input Output | Computing |
| Super Input Output | Computing |
| Service Information Object | Computing |
| Start Input Output | Computing |
| Shareable Interface Object | Computing |
| Server Indirection Object | Computing |
| Scalable Input Output | Computing |
| Storage Input Output | Computing |
| Security Information Object | Computing |
| Simultaneous Interface Operation | Computing |
| Stanford Internet Observatory | Computing |
| Scalable Input/ Output Initiative | Computing |
| Secure Identity Object | General |
| Semanticscience Integrated Ontology | General |
| Security Intelligence Operations | General |
| Strategise Implement Operate | General |
| Serial I O | General |
| Saptam in One | General |
| s for Input Output | General |
| Shock Induced Oscillation | General |
| Sea Ice Outlook | General |
| Speelgoed Industrie Overijssel | General |
| Summary Instalment Orders | General |
| Skin Innovation Overnight | General |
| Smart Inbound Optimization | General |
| Swarm Intelligence Optimization | General |
| Service Improvement Operations | General |
| Societas Internationalis Odontologica | General |
| Standard I O | General |
| Single Image Output | General |
| Senior Investigating Officer | Governmental |
| Section of International Organisations | International |
| Serious Inquiries Only | Jobs |
| Society for Integrative Oncology | Medical |
| Society of Interventional Oncology | Medical |
| Standard Installation Organization | Military and Defence |
| Senior Intelligence Officer | Military and Defence |
| Special Information Operations | Military and Defence |
| Siouan Languages | Regional |
| Smithton, Tasmania, Australia | Regional |
| Serial Input/output | Space Science |
| Systems Integration Office | Space Science |
| Subscribers In Operation | Telecommunication |
