By Angus McDowall
DUBAI (Reuters) - When Saudi Arabia's King Abdullah had a back operation on Monday, the weekly cabinet meeting was instead chaired by Prince Nayef, indicating the likely path for any future transfer of power in the world's largest oil exporter.
The surgery on the octogenarian monarch was successful, but with his immediate heir, Crown Prince Sultan, also in his 80s and experiencing health problems that have kept him in the United States since June, there is an increasing focus on the kingdom's leadership plans.
"They have a system," said Qainan al-Ghamdi, a former editor of al-Watan daily newspaper. "After the king comes the crown prince and after him Prince Nayef. So if anything happens, there is no problem."
To outsiders, the al-Saud ruling family's succession process often appears forbiddingly opaque. But behind the ornate gilt doors of Riyadh palaces, the senior most princes in a family thousands strong have long sketched out the next steps in a complex dance of power.
Unlike in European monarchies, the line of royal succession does not move directly from father to eldest son, but has passed down a line of brothers born to the kingdom's founder King Abdulaziz Ibn Saud, who died in 1953.
So far five brothers have become kings and around 20 are still alive, but only a few of those are thought realistic candidates to rule the country where Islam was born some 14 centuries ago. Some have already been passed over or renounced their claims to rule.
Under rules drawn up soon after Abdullah became king in 2005, succession decisions should lie with an "allegiance council" of the ruling al-Saud family.
The council has 34 princely members who each represent a family of a son of Ibn Saud and can cast one vote each to choose the next heir to the throne.
However, the mechanism has not yet been put to the test and while the next two or three moves down the royal ladder seem fairly straightforward, there will be keen interest in how the council handles a more complex succession decision in the future.
"The system has worked well in the past but there are new challenges," said Khaled al-Maeena, editor at large of the English language daily Arab News. "But even 10 years down the line it will go smooth. This is a hallmark of the al-Saud."
To avert a repeat of the situation that unfolded after King Fahd fell ill, when Abdullah's leadership was fettered by his ambiguous position as de facto regent but without the formal title, the council has the power to remove a king or crown prince who is too sick to rule.
Given the old age of both Abdullah and Sultan, who in a 2009 diplomatic cable released by WikiLeaks was described as "to all intents and purposes incapacitated", the clause might prove an important failsafe in a country where power emanates from the top.
Nayef, the kingdom's veteran interior minister, was named second deputy prime minister in 2009 and is widely assumed to be second-in-line to become king behind Abdullah and Sultan.
His emergence as the most active senior member of the ruling family has caused liberal Saudi Arabians some disquiet, due to his reputation as a steely conservative with close ties to the powerful clergy of the kingdom's austere Wahhabi school of Islam.
However it is possible that as king Nayef may be more likely to move toward the center ground of a political system that prizes consensus -- meaning the slow process of economic and social reforms initiated by Abdullah might continue.
The most powerful bloc within the variegated ranks of the al-Saud is thought to comprise the sons born to Ibn Saud by his favorite wife Hassa bint Ahmed al-Sudairi: the so-called "Sudairi Seven".
They included the late King Fahd, Crown Prince Sultan and Prince Nayef, as well as the powerful Riyadh Governor Prince Salman who is widely seen as next in line after Nayef. Three other brothers include a former defense minister, a deputy defense minister and a deputy interior minister.
To many analysts the key question is what will happen when the succession moves beyond the sons of Ibn Saud to one of his grandsons.
That decision might not be made for a decade or more, but outside observers already see the emergence of a handful of contenders who appear better qualified to rule than their cousins.
There are no formal rules to dictate how the generational transition will be made other than through Abdullah's allegiance council. But any candidate would need broad support among the family as well as a strong record of political experience.
That might point to one of the Sudairis, such as Fahd's son Mohammed, who is governor of the Eastern Province, Sultan's son Khaled, who is deputy defense minister and led Saudi forces during the 1991 Gulf War, or Nayef's son Mohammed, who as deputy interior minister was partly responsible for the successful suppression of an al Qaeda uprising six years ago.
Another potential candidate among the third generation of the al-Saud is Prince Khaled al-Faisal, son of the former King Faisal and well regarded governor of Mecca Province, one of the most prestigious jobs in the country.
Prince Miteb bin Abdullah, the son of the present king, has inherited his father's position as head of the Saudi Arabian National Guard, a military unit that stands separate to the ordinary armed forces and defends against the risk of coups d'etat.
(Reporting By Angus McDowall; editing by Sami Aboudi and William Maclean)