Iran's crude exports are set to drop by about a quarter in December from the preceding month to the lowest since tough sanctions were applied this year, shipping sources said, as the OPEC-member comes under pressure to curb its nuclear programme.
Oil shipments by Iran have more than halved in 2012 due to U.S. and European sanctions on its oil trade, straining Tehran's finances, pressuring its currency and igniting inflation.
Most of the crude would have gone to energy hungry Asian buyers - China, India, Japan and South Korea -- with the drop in December shipments from November representing a loss of about $800 million for Iran at current oil prices.
China, Iran's top trading partner, is expected to drive the cut by lifting the lowest volume for the year, said the sources, who declined to be identified because of policies on talking to the media.
Iran's customers, including Turkey, the only non-Asian buyer, will lift 834,000 barrels per day (bpd) of crude in December compared with 1.08 million bpd in November, an industry source with direct knowledge of Tehran's shipping plans said.
The December number puts Iranian crude imports by Asia's top buyers for the full year at about 1.06 million bpd, down roughly a quarter from a year ago, according to Reuters calculations.
The United States, which is due to decide this month on whether to renew a 180-day waiver from sanctions for importers of Iranian oil, wants to see buyers progressively cut purchases.
Washington says Tehran is enriching uranium to levels that could be used in nuclear weapons. Iran says the programme is for peaceful purposes.
The architects of U.S. sanctions legislation, Democratic Senator Robert Menendez and Republican Senator Mark Kirk, have urged the White House to require oil importers to reduce purchases by 18 percent or more to qualify for further exemption.
Of Iran's top four clients in Asia, Japan has already secured its exemption while India, South Korea and China are expected to get an exemption this month.
Market nerves over the impact of sanctions on supply pushed Brent crude futures to a high of $128 a barrel in March and have kept the benchmark over $100 for most of this year.
Iranian exports took a deep hit from July once European Union sanctions banning insurance cover for ships carrying Iranian oil came into force. Shipments recovered in October to 1.3 million bpd from 1.0 million seen in the two previous months, the International Energy Agency said.
December loading by China is put at about 242,000 bpd, the lowest this year. Including November's estimated 382,000 bpd, the average rate for the two months would be around 312,000 bpd, nearly 25 percent below the January-October rate of 424,000 bpd.
China, India and South Korea are asking Iran to ship the oil because they are unable to secure insurance cover on tankers, but delivery has often been delayed as the Iranian fleet is stretched with many tankers being used as floating storage.
"It is still the same problem, but one that is getting worse," said a Chinese buyer of Iranian oil. "The journey between Iran and China has in some cases been stretched to 60 days from the previous 40 days."
India's loading for December is estimated at 119,400 bpd compared with 275,000 bpd in November. Asia's third-largest economy is the only one to have raised imports in the first 10 months of the year, by about 7 percent to 328,000 bpd.
Japanese refiners are set to load about 186,000 bpd in December, up around 21 percent from 154,000 bpd, and all the cargoes are due to reach in January, industry sources said.
The rise in December loading reflects Japan's increase in Iranian crude purchases during the winter due to higher demand for heating. Since it won its first waiver from U.S. sanctions in March, Japan has cut imports each month by more than a quarter except for an increase of 6.8 percent in June.
South Korea's loadings in November and December will be around 200,000 bpd, in line with its commitment to lift under annual contracts. It became the first major Asian consumer of Iranian crude to announce a halt in imports due to the EU ban. Seoul imported no crude oil from Iran in August and purchases resumed in September.
Taiwan's Formosa is scheduled to lift about 61,000 bpd in December, after the island completely halted imports from April. Taiwan's Iranian imports averaged 30,250 bpd in 2011.