Saudi Arabia's King Fahd died today and Crown Prince Abdullah was swiftly pronounced monarch of the world's largest oil exporter.
A Saudi source said the kingdom's oil policy would not change.
Diplomats said they expected no major shifts in foreign policy under King Abdullah, who is at least 80 and has run day-to-day affairs since a stroke debilitated King Fahd in 1995.
Saudi Arabia's King Fahd, who died this morning
"With deep sorrow and pain, the royal court... mourns the death of The Custodian of the Two Holy Mosques King Fahd due to illness," said Information Minister Iyad bin Amin Madani, reading an official statement on state television.
King Fahd, who was believed to be 83 and had been in poor health, had entered hospital on May 27th with acute pneumonia.
US crude oil jumped to $61 a barrel after the news.
The Saudi source said Riyadh would adhere to its long-standing oil policy aimed at keeping global markets well supplied to stabilise prices.
"I am sure nothing will change regarding Saudi Arabia's oil policy," the source said.
The Saudi stock market, the largest Arab bourse, briefly suspended trading and was down almost two per cent after reopening.
A Saudi official said King Fahd's funeral would take place tomorrow to give time for foreign dignitaries to take part.
King Abdullah, the fifth son of Saudi Arabia's founder King Abdul-Aziz to ascend the throne, is a cautious reformer who has overseen modest economic and political liberalisation.
In the past two years, the kingdom has faced a violent al-Qaeda campaign to end seven decades of the royal family's rule in Saudi Arabia, home to Islam's holiest shrines.
King Fahd ascended the throne of one of the world's richest nations in June 1982, at the height of Saudi Arabia's petrodollar boom and reigned for 23 years, through three regional wars and, in his final years, al-Qaeda militancy.
His strong alliance with Washington and his decision to allow US forces to deploy in Islam's birthplace in 1990 enraged Saudi-born al-Qaeda leader Osama bin Laden.
Bin Laden has vowed to depose the Saudi royal family who he blasted as US "agents and stooges" and whose rule he described as an "extension of the crusader wars against Muslims".
US troops remained until the 2003 invasion of Iraq and the overthrow of Iraqi President Saddam Hussein. By that time the September 11th, 2001 attacks, carried out mainly by Saudi hijackers, had clouded the relationship with the United States which had been King Fahd's foreign policy cornerstone.
Suicide bombings in the capital Riyadh two years later brought insurgency home, while the strategic alliance with Washington, centred on oil and Gulf security, was in crisis. But ties partly recovered after intense diplomacy by both countries and Riyadh's support for the US "war on terror".
Taoiseach Bertie Ahern sent a message of sympathy to King Abdullah. "On my own behalf, and on behalf of the Government of Ireland, I wish to convey our deepest sympathy on the demise of your dear brother, the Custodian of the two Holy Mosques, King Fahd bin Abdul Aziz Al-Saud," he said.
"During his reign, your country has enjoyed a time of great advancement and prosperity and, under his leadership, has played a strong and important role in the promotion of peace in the Middle East and in the wider world. We feel sure that this legacy will continue under your wise and prudent guidance.
"At the same time, I would like to offer my best wishes to Your Highness as you assume your new duties as King of Saudi Arabia, and assure you of the wish of the Government of Ireland to continue to pursue its close cooperation with your Kingdom for the greater benefit of our two nations."