RIYADH, Saudi Arabia – OPEC's 13 member nations opened a summit Saturday night with a sumptuous celebration of $100-a-barrel oil and a warning from Venezuelan President Hugo Chávez that the price could double if the United States attacks Iran.

"If the United States is crazy enough to invade Iran or makes an aggression against Venezuela again, the price of oil will not be $100 but maybe $200," Mr. Chávez told his fellow oil-exporting leaders, gathered in a magnificent palace.

Iran's defiance of U.N. demands to halt its nuclear program has many in this part of the world worried that the Bush administration may launch a military strike aimed at crippling what appears to the West to be an effort by Tehran to develop nuclear weapons.

Mr. Chávez accused the United States of trying to break up OPEC in the 1980s and 1990s and said the U.S.-led invasion of Iraq, an OPEC member, was part of an American campaign to dominate global oil supplies.

He has often blamed the White House for a failed coup that briefly ousted him from power in 2002, and last week he said Spain, a U.S. ally, was also aware of the plotting against him. In a widely reported incident, Spain's King Juan Carlos told Mr. Chávez to "shut up" at the Ibero-American Summit in Chile, a public rebuke that infuriated the Venezuelan president.

At the Mideast summit, Saudi Arabia's King Abdullah, the only other OPEC leader to address the group Saturday evening, ignored Mr. Chávez's plea for a more political OPEC but agreed with the Venezuelan leader that $100 oil is not even what the world was paying in the early 1980s, once inflation is considered.

"The present price of petroleum will not have reached its actual price of the 1980s," King Abdullah said.

Oil was trading closer to $90 a barrel late last week after topping $98 earlier.

The summit opened in a huge ornate chamber lit with 11 spectacular chandeliers. The leaders gathered at a horseshoe-shaped table at least 35 yards in diameter. Mr. Chávez, who hosted OPEC's 2000 summit in Caracas, handed the chair to King Abdullah with a boast that oil was $10 when the leaders met in Venezuela but almost $100 today.

The Saudi monarch honored three researchers and three journalists for helping the world gain a better understanding of petroleum, including Daniel Yergin, author of a history of oil called The Prize.

Dr. Yergin, who chairs Cambridge Energy Research Associates of Cambridge, Mass., accepted the award but afterward offered a gentle riposte to the king's comment on the history of oil prices.

"That [$100] was an actual price for a very brief period in the 1980s," Dr. Yergin said.

Cambridge Energy recently published an analysis saying oil's previous peak was in April 1980, when it hit $39.50 a barrel. After factoring out inflation and the decline in the value of the dollar, that price is equivalent to $99.04 today, Dr. Yergin said.

With Ecuador rejoining the organization and Angola present at its first summit, OPEC now has 13 members – Saudi Arabia, Kuwait, Iraq, Iran, Qatar, the United Arab Emirates, Indonesia, Algeria, Libya, Nigeria, Angola, Venezuela and Ecuador.

Libyan leader Moammar Gadhafi was the only absentee. U.S. and Saudi officials say Mr. Gadhafi was behind a plot to assassinate King Abdullah in 2004.

The foreign, finance and oil ministers of OPEC's member states have been meeting here for two days to hammer out a communiqué, with Iran and Venezuela pressing for language moving OPEC away from dollar pricing and toward a basket of currencies.

Iran already takes payment for its oil exports in euros and yen to protect itself from further U.S. sanctions over its nuclear program. A move to other currencies would weaken demand for dollars around the world and further depress the U.S. currency.

Saudi Arabia's foreign minister, Prince Saud al-Faisal, argued at a meeting of the ministers that if OPEC declared that it was moving away from the U.S. currency, it could trigger a dollar collapse.

His remarks became public because a television microphone in the meeting hall was left on.

After the awards presentation, the Saudis moved the 1,200 guests to a palatial banquet hall for a six-course meal featuring both traditional Saudi foods such as lamb and hummus and more extravagant dishes such as Canadian lobster and cappuccino mousse.