Bad weather cut oil exports from Iraq's Basra ports to 960,000 barrels per day (bpd) on Sunday from 2.35 million bpd a day earlier, a shipping source said.
"High winds in the Gulf are preventing loaded ships from leaving the port on Sunday," the source said.
Iraq exports the bulk of its crude from the southern ports at the Gulf and bad weather and technical issues have made it difficult for the OPEC member to keep shipments steady.
Iraq's oil exports fell to 2.34 million barrels per day (bpd) in December from 2.62 million bpd in November due to a rough weather and technical problems with a single point mooring terminal in the Gulf.
Lower oil shipments from autonomous Iraqi Kurdistan in December also pushed down total average exports due to disagreement over payments between Baghdad and the self-governed Kurdish enclave in the north.
"Bad weather is one of the major issues that could affect average exports for this month. I can predict a low figure for January also because of the weather," an official with Iraq's state-run South Oil Company (SOC) said.
Exports from the south, the country's main crude shipment point, have risen steadily, bringing Iraq closer to its highest export level in decades.