A leading global energy monitor fears there may not be enough oil to slake the world's thirst _ and is preparing a landmark forecast that could reverberate through the global economy even as major companies announce fuel-related cutbacks.

The International Energy Agency is studying depletion rates at about 400 oil fields in a first-of-its-kind study of world oil supply, chief economist Fatih Birol said.

"We are entering a new world energy order, " Birol told The Associated Press.

Market analysts call the Paris-based IEA the world's most reliable independent source of oil information and welcomed its decision to undertake a deep study of oil supplies.

But the IEA's new forecasts are likely to further upset markets. Oil prices hit an all-time high Thursday above $135 a barrel before falling back.

Less oil would mean even higher prices for everything from gasoline to food. Already, airlines squeezed by jet fuel costs are bleeding profits and predicting cutbacks and industry upheaval. Ford Motor Co. said Thursday it was cutting production of gas-guzzling sport utility vehicles and forecast more rough times ahead.

Birol said the IEA study, whose results will be released in November, was prompted by concern about the volatility of world oil markets and uncertainty about supply levels.

"The prices are very high, and demand did not respond in the last few years as much as one would have expected," Birol said. "The growth in terms of production was not great. We did not see enough investment."

The spurt in oil prices Thursday came after a report in the Wall Street Journal that the IEA was planning to lower its forecast for long-term world supply.

Birol would not speculate on whether the forecast, which will predict supplies through 2030, could go sharply downward. "We will see," he said.

The IEA's past forecasts put oil supply at about 116 million barrels a day in 2030, up from 87 million barrels a day now.

"Although the agency's official assessment isn't expected until later this year, the market's interpretation is that global supply may be significantly tighter than previously projected by the major oil market monitors," said Jim Ritterbusch, president of energy trading advisory service Ritterbusch and Associates in Galena, Illinois.

Birol said oil companies and governments have cooperated with IEA experts preparing the report, but added, "It is not an easy task. It is the first time this is being done in the public domain on such a scale."

Simon Wardell, oil analyst at Global Insight in London, was skeptical that the IEA would get a complete picture from "countries that are very closely guarded" such as Saudi Arabia, the No. 1 producer.

That is important because Birol said one of the key shifts coming up is that the world will become increasingly reliant on national oil companies instead of multinational ones.

"Up to now, we have seen that the international oil companies were responsible for bringing a big chunk of the oil to the markets. Now, in many cases, since existing reserves are declining, a big part of oil will need to come from national oil companies. And they have their own conditions, their own context."

Birol called for greater investment everywhere. Continued...