“Saudi Arabia marshaled a seemingly impressive coalition for its air war on Yemen. In addition to its Sunni allies in the Gulf, Riyadh roped in partners ranging from Sudan to Morocco, and even far-off Senegal. However, one ally of the kingdom is sitting out the war: Oman.
Indeed, Oman is the only Arab monarchy that declined to participate in the Saudi-led Operation Decisive Storm in Yemen. By not deploying its military to strike Houthi targets in its southern neighbor, Oman is further demonstrating that it is the Gulf Cooperation Council (GCC) member most independent from Riyadh’s sphere of geopolitical influence — and most committed to cooling regional sectarian tensions.”
http://www.al-monitor.com/pulse/originals/2015/05/oman-response-yemen-conflict.html
IR Theory & Practice 