When King Salman bin Abdulaziz succeeded King Abdullah last month, the Kingdom of Saudi Arabia edged one step closer towards a succession crisis.

US Secretary of State John Kerry with Omanu Sultan Qaboos bin Said, May 2013. (Flickr/US State Dept.)

There remain two more sons in the house of national founder, King Abdulaziz. Saudi Arabia is the only absolute monarchy that operates through agnatic primogeniture, whereby hereditary succession proceeds horizontally through male siblings rather than vertically through descendants.

King Salman, aged 79, is the 35th son of Abdulaziz. His Crown Prince and brother Muqrin, aged 69, is likely the last of the line (Prince Ahmed is between them in age, but has not yet been designated an the order of succession). It may not be a long wait, as King Salman is rumoured to be in ill health. Prince Muqrin is healthy but may lack the necessary support of the Allegiance Council as his mother was a Yemeni, not a Saudi princess.

Regardless, the crown must eventually pass to the next generation. But to whom? King Salman has named Prince Muhammad bin Nayef as the new Deputy Crown Prince, the first grandson of Abdulaziz to be designated in the line of succession. However, it is doubtful that this will go unchallenged given the number of hopefuls. Just as Mark Twain once complained that he couldn't 'throw a rock in any direction without hitting a captain of (t)his ship', the same could be said of princes in Saudi Arabia. By best estimates, they number over 4000.

In neighbouring Oman, the number of princes is exactly zero.

As the next Gulf country likely to experience a rare succession, Oman represents a more unusual problem. Sultan Qaboos, who is closely associated with the economic modernisation of the country, has yet to designate an heir in more than 40 years on the throne. Now in poor health (reported to be terminal cancer) and receiving extended medical treatment in Germany, the possibility of a power vacuum is real; the popular Sultan has no children, no living siblings and no nieces or nephews.

It is a unique problem for hereditary regimes in the Gulf, and one in which the West, including Australia, has a vital interest.

Oman under Sultan Qaboos has become known as a diplomatic linchpin in the region, most recently hosting unofficial talks between Iran and the US on the peaceful resolution to Tehran's nuclear ambitions. It also hosts US and other allied military assets, has successfully negotiated the return of hostages held by al Qaeda in Yemen, paid the bail for US hikers detained on espionage charges in Tehran and secured the release of British naval personnel captured by the Iranian military in 2007. And Muscat hosts the only intergovernmental organisation in the world in which Israel, the Palestinian Authority and Jordan sit at the same table on a regular basis: the Middle East Desalination Research Centre.

As guardian of the Straits of Hormuz, through which 30% of all seaborne oil transits (and which lie wholly within its territorial waters), Oman's economic and political stability is of international concern. Yet the process of succession is far from comforting.

Oman has one of the most curious succession plans in the world. Childless and divorced, Sultan Qaboos will leave his choice for the next Sultan in a posthumous letter to his family. According to the Basic Law, swiftly codified in 1997 after the Sultan was involved in a car accident, the royal family has three days to reach a consensus. Barring this, his letter will be opened and one of the two names contained therein will be announced as Sultan. Putting aside the potential for failure in an untested process with multiple nominees (the names are contained in several letters spread across two countries for safekeeping), the problem remains that few members of the Sultan's family are considered suitably experienced for the post.

The Sultan, more than any other regent in the Gulf, is an absolute monarch. He serves as prime minister, head of the military, minister for foreign affairs and chairman of the central bank. Even each branch of the military reports personally to him. Although Sultan Qaboos, affectionately called 'HM' (His Majesty), is universally popular, the same cannot be said for his possible successors. Omanis are not familiar with the rest of the small royal family, all of whom maintain a low public profile.

Meanwhile, domestic expectations for the successor continue to grow.

Both Oman and Saudi Arabia experienced some protests during the Arab Spring. The majority of the protests called for reform rather than an end to the monarchical systems that have overseen the economic transformation of both countries. However, with the recent shift in the oil markets (the IMF warned that GCC exporters could lose US$300 billion due to falling oil prices in 2015), a successor may face an immediate budget shortfall.

Though Saudi Arabia has some leverage through its extremely generous sovereign wealth fund, Oman (not a member of OPEC) has a far smaller nest egg. Government spending in both countries has increased by more than 50% over the last five years owing to increases in the minimum wage, unemployment benefits and generous financial packages distributed after the Arab Spring.

Low oil prices have not yet stymied expenditure. Last week, the new Saudi King distributed a two-month income bonus to all public servants, retirees, students and social service recipients.

The perception of sound economic management and stable governance is crucial to the continued growth of foreign direct investment in the region, which both countries court with great enthusiasm in an effort to diversify their economies beyond hydrocarbons. Succession done poorly would be extremely damaging for business.