"No one really knows," Adams told reporters who traveled with him to the G20 deputies gathering in the Chinese port city of Dalian. "And that's disconcerting -- the uncertainty around our inability to really forecast what the oil price is going to be six months from now or a year from now but, more importantly, what their macroeconomic effect is going to be."

The G20 includes the Group of Seven club of rich nations along with key emerging economies like this year's host, China, as well as India and Brazil. Its membership takes in not only key oil-consuming nations like the United States and Japan but also producers like Saudi Arabia and Canada.

Thursday's closed-door meeting featured extensive talks on how to raise oil output while recognizing "there are bottlenecks and constraints all up and down the supply chain" that make it hard to quickly adjust supplies of raw and finished energy products, Adams said.

The devastation wrought by Hurricane Katrina on the US Gulf Coast, site of much of America's refinery capacity, only highlighted the importance of the issue.

Adams said some G20 officials noted that no US refineries have been built since the late 1970s and said the United States must address its ability to turn crude oil into finished products like gasoline and heating oil.

"There are more questions than there are answers," Adams said, adding that the government must take steps to encourage more refinery capacity.

"If there's a market failure then obviously there is a government role," he said. "There may be a market failure in the perception that the cost of building a refinery may be so large that it has precluded any refineries from being built."

Adams said the Bush administration has conducted "inter-agency policy exercises" over the past year to identify why refinery-building stopped in the 1970s and to see how to encourage a resumption.

Adams, recently confirmed in his new post, was on a week-long trip to Japan and China and was due to return to the United States on Friday.

In Tokyo, he said Asian economies should try to grow by strengthening domestic consumption rather than through exports, and said the United States expects China to let its yuan currency appreciate further on the way to establishing a freely floating exchange rate.

Adams said several G20 participants noted China's move in July to scrap a decade-old peg between the yuan and the US dollar, letting it rise about 2 percent, but wanted more.

"There were a number of statements today acknowledging the move by the Chinese and welcoming the move and urging the Chinese to do what they have said they plan on doing, which is to put in place greater flexibility over time," he said.

Adams met separately on Wednesday with China's Vice Finance Minister, Li Yong, but declined to give details. "We discussed a number of issues pertinent to our relationship. You can figure out what they are."

US manufacturers have long argued the yuan was undervalued by as much as 40 percent, making it hard for the United States to compete, which prompted some US lawmakers to threaten to impose tariffs on Chinese imports.

China's modest revaluation helped soothe some of the anger but lawmakers want the yuan to rise further, something Adams implied the White House also wants.

"In our continued support for their move, there was implied in that an assumption that there would be greater liberalization over time," Adams said, adding: "That is also reflected in their own public comments so I take them at their word that is the trajectory that they are on."

The meeting of G20 deputies was to map out an agenda for a mid-October meeting in China of Group of 20 finance ministers and for semi-annual meetings on Sept. 24-25 of the International Monetary Fund and World Bank in Washington.

Finance chiefs from the G7 -- the United States, Britain, Canada, France, Germany, Italy and Japan -- will meet in Washington a day before the IMF gathering.

Adams said there was a growing desire to give Asia's fast-growing economies more say in the affairs of the international lenders.

"There seems to be a number of G7 countries today who believe that this is an important endeavor so that the institutions reflect the relative weights of the various economies."