Oman

The ruling system is Sultani (Royal), hereditary through the male descendants of Sultan Turki bin Said bin Sultan, in accordance with the following provisions:
– Title to the throne passes from the Sultan to His eldest son, followed by the eldest son of this son, and by a similar process afterwards. If the eldest son dies before the title to the throne passes to him, the title to the throne passes to his eldest son, regardless of the deceased having brothers.
– If he who has title to the throne has no sons, the title to the throne passes to his eldest brother. If he has no brothers, it passes to the eldest son of his eldest brother. If his eldest brother has no sons, it passes to the eldest son of his other brothers, in accordance with their seniority in age.
– If he who has title to the throne has no brothers and no sons of brothers, the title to the throne passes to the paternal uncles and their sons in the order prescribed in the second clause of this article.
Whoever assumes the title to the throne must be Muslim, rational, and a legitimate son of Muslim Omani parents. (Art. 5)

A royal order shall be issued to appoint the person to whom the title to the throne belongs to in accordance with the text of article 5 of this statute as crown prince. This royal order shall specify the competences and the responsibilities assigned to him.
... (Art. 7)

The Sultan is the head of the state, its most supreme representative, and its supreme commander. His person is inviolable, respect for Him is a duty, and His command is obeyed. He is the symbol of national unity and the vigilant guardian and protector of the state. (Art. 48)