By Andrew Hammond and Simon Webb

RIYADH (Reuters) - The prospect of $100 oil and what OPEC can -- or cannot -- do about it will loom large as leaders of major oil exporters including Saudi Arabia, Venezuela and Iran meet in Riyadh this week.

When the OPEC heads of state last met in 2000 oil was at $30, and memories still fresh of a slump to $10 in 1998 that forced them to make painful spending cuts.

Now their state coffers are bulging after years of bumper revenues and it is oil consuming countries' turn to feel the pinch.

But oil ministers of the Organization of the Petroleum Exporting Countries say they have little sway over rising prices, and that boosting supply would have minimal impact.

They say the market is well supplied and the high price is due to international tensions, huge investment flows into the market, record dollar weakness and refinery capacity constraints.

Still, the world's largest oil exporter Saudi Arabia will want to show concern for the effects of high prices on the world economy and its ally the United States.

Saudi Oil Minister Ali al-Naimi said on Sunday that oil ministers would discuss raising oil output again at an upcoming meeting.

OPEC's next formal ministerial conference is scheduled for for December 5 in Abu Dhabi.