Saudi Arabian Interior Minister Prince Nayef bin Abdulaziz is expected to be named crown prince following the death of his half-brother, Prince Sultan, 85.

But the royal succession in the oil-rich kingdom could be complicated by the generation of aging princes who are contenders to the throne, most of them in their 80s and in poor health.

King Abdallah, believed to be 89 or 90, is also ailing and could die soon. He became monarch in 2005 following the death of his half-brother, King Fahd.

With Saudi Arabia locked in an escalating cold war with Iran, its regional rival, buffeted by the political upheavals of the Arab Spring and the waning power of the United States, the kingdom's longtime protector, a succession crisis is the last thing the House of Saud needs.

The new crown prince will be chosen by the Allegiance Council, formed by Abdallah in late 2006, replacing the informal mechanism by senior figures in the royal family that has been employed since the death in 1953 of King Abdelaziz, who founded Saudi Arabia in 1932.

The powerful Sudeiri clan, the sons of Abdulaziz's favorite wife, have dominated the royal household and the succession process for years.

Abdallah, the son of another of Abdelaziz's wives, has no full brothers holding powerful positions but he has put his sons in key posts.

His most prominent son, Mitab, recently took command of the Saudi national guard, a largely Bedouin counterweight to the military controlled by Sultan that Abdallah had built up over the years.

His rivalry with the Sudeiris is the principal schism within the royal house, which embraces some 7,000 princes.

A third clan, the family of former King Faisal which includes the foreign minister, Prince Saud, and Faisal's son Prince Turki, the Saudi intelligence chief in 1977-2001, has been weakened in recent years.

The council, designed by Abdallah to modernize and widen the succession process, consists of the 35 most senior princes, the 16 surviving sons of Abdulaziz -- he had around 40 by various wives -- and 19 of his grandsons.

But it hasn't been tested. The word is that it will endorse Prince Nayef, the kingdom's hard-line security chief and the scourge of al-Qaida, as the new king-in-waiting.

If Nayef, who's 80 and said to be recovering from a bout of cancer, does become king, he's likely to be the last of Abdulaziz's sons to occupy the throne -- and may not last long as monarch if he does.

"His full brother, Salman, 74, the governor of Riyadh province and every foreign ambassador's favorite to be king, is also apparently disqualified by a weak heart," observed Simon Henderson, a veteran observer of Saudi politics from the Washington Institute for Near East Policy.

Next time around -- and given the condition of the aging sons that may not be too far in the future -- rather than choose another geriatric, the council is expected to decide it's time to make one of Abdulaziz's grandsons king.

That would likely signal a new era in Saudi Arabia. Abdulaziz's sons have monopolized the highest offices of state for decades. Prince Sultan had been minister of defense and aviation since 1962. Prince Saud has been foreign minister since 1975.

The next generation, meantime, is champing at the bit for its turn to be in power.

"What makes this internal dynamic far more critical is the regional unrest that broke out in early 2011 and has altered the regional landscape and led to the toppling of three different autocratic Arab rulers," the U.S. global intelligence consultancy Stratfor notes.

"While Saudi Arabia has remained immune from the contagion due to its unique socio-political economic realities, the succession issue does complicate matters for Riyadh.

"The Arab unrest, coupled with the threat from a rising Iran and its Arab Shiite allies at a time when U.S. forces will be exiting Iraq by Dec. 31 places further strain on the Saudis," Stratfor observed.

"Saudi Arabia is already heavily involved in managing the unrest in Yemen and Bahrain … and would like to see regime-change in Syria."

Stratfor concluded: "Historically, the Al Saud family has proven to be extremely resilient in overcoming many challenges but given the unique constellation of domestic and international circumstances, we're now in uncharted waters."