Saudi Arabia said on Friday a committee of princes will vote on the eligibility of future generations of kings and crown princes, in an apparent bid to formalise the succession process.
The system will not take effect until Crown Prince Sultan, heir to King Abdullah, becomes king, a statement from the royal court said.
The committee will be made up of sons and grandsons of late King Abdul Aziz al-Saud, founder of modern Saudi Arabia and father of the current king and crown prince, said the statement signed by King Abdullah.
It did not specify the size of the committee, to be called the Allegiance Institution. It will be chaired by the eldest son or grandson of King Abdul Aziz.
The step was taken in the "general interest", it said. It is part of an amendment of the Basic Law, the name given to the absolute monarchy's constitution.
The previous system gave the king full prerogative to name the crown prince although Western diplomats say such decisions are often debated within the royal circle.
Under the new system the Allegiance Institution will have a say in the appointment of a crown prince suggested by the king. If the institution rejects the nominated crown prince, it may vote for one of three princes the king nominates for the title.
The appointment of the new crown prince must be done within 30 days of the accession of a new king, the statement added.
All of the Allegiance Institution's meetings are to be held behind closed doors.
Five members of the institution will form a Transitory Ruling Council which would take over the running of state affairs for a maximum period of one week if neither the king nor the crown prince are fit to rule the country, it said.
The Transitory Ruling Council will not enjoy prerogatives affecting state institutions, such as dissolving the government or the country's self-styled parliament, and will not be able to amend the Basic Law or any "laws that are linked to the rule".
Mohammed al-Zulfa, a member of the advisory Shura Council, said the move would ensure "that only the eligible sons of Kind Abdul Aziz will get to rule" the world's top oil-producing nation. "It will bring inner peace among members of the royal family and among citizens. The system is clear now," he said.
Shura Council is a sort of parliament whose members are appointed by the king.
"This is a turning point that will ensure the continuity of the ruling family," Zulfa told the Saudi-funded al-Arabiya Television.
"King Abdullah has ... made this decision at a crucial time, the kingdom is going through a phase of change and development and he wanted society to be in safe hands in the future".