Oil pipelines from Iraq have already shut down
Saddam Hussein has announced an immediate halt to oil exports for 30 days in protest at Israel's military action against the Palestinians.
Exports from Venezuela have been almost halted by industrial action in protest against the company's new board of directors.
Iraq and Venezuela jointly export about 4.5 million barrels a day, with Venezuela a major supplier to the US market.
Emergency meeting
Ali Rodriguez, head of the Organization of Petroleum Exporting Countries, warned that the loss in global exports could lead directly to an oil crisis.
Mr Rodriguez would not say whether Opec intended to meet any shortfall in supply, but said measures would be discussed to maintain market stability.
He said he did not know if Opec ministers would call an emergency meeting.
The standstill in Venezuela looks set to worsen following the decision by the country's President, Hugo Chavez, on Monday to sack seven striking executives at Petroleos de Venezuela, the state oil company.
Price surge
Refining at Venezuela's 950,000-barrels per day Paraguana refinery complex - one of the world's largest - was at 50% percent on Monday, with other refineries operating at lower-than-usual production levels.
Iraq is cutting exports for 30 days, with a review of their decision due after that time.
The action comes as Israel continues its military operations in the West Bank.
Oil prices surged to more than $27 a barrel after the declaration.
Iraq currently exports about two million barrels of crude oil a day under a United Nations programme permitted as an exception to Gulf War sanctions.