At 10:40 am Singapore time (0240 GMT), ICE October Brent crude futures were up 12 cents/b (0.16%) from Monday's settle at $73.87/b, while the NYMEX September light sweet crude contract was unchanged over the same period at $69.01/b.
On top of that, Iranian President Hassan Rouhani has threatened to disrupt regional oil production and exports if the Trump administration follows through with oil sanctions.
A first batch of US sanctions against Iran, which shipped out nearly 3 million barrels per day (bpd) of crude in July, officially came into effect at 12:01am US Eastern time (0401 GMT) on Tuesday.
US sanctions on Iran's energy sector are set to be re-imposed after a 180-day "wind-down period" ending on November 4.
Iran's fleet of very large crude carriers, or VLCCs, and Suezmax tankers - the largest that can fit fully-laden through the Suez Canal - has always played an important role in delivering Iranian crude to customers, but it is increasing as insurers and worldwide shipping companies react to the sanctions snap-back.
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Since late 2016, the Organization of Petroleum Exporting Countries and other nations, including Russia, Kazakhstan and Mexico, have managed the oil market, giving birth to a group popularly known as OPEC+. That is fast changing as Iran seeks to maintain deliveries to Turkey amid US sanctions. A trade spat between the U.S. and China has kept oil from rebounding from a seven per cent plunge last month. The US will also target business conducted by foreign financial institutions with the Central Bank of Iran. "The reports that Saudi Arabia's production actually dropped in July continue to provide support for the market".
Oil prices rose on Monday after Saudi crude production registered a surprising dip in July and as American shale drilling appeared to plateau.
Market analysts warned that oil prices could surpass $90 if Iranian supplies of around 2.4 million barrels per day (bpd) are disrupted.
Output was expected to rise 1.31 million bpd to 10.68 million bpd in 2018, lower than last month's forecast of growth of 1.44 million bpd to 10.79 million, the EIA said.
Indian crude imports from Iran continued in the range of 200,000-250,000 b/d during the previous sanctions on Iran.
"We view that it is very unlikely that the USA administration will be successful in reducing Iranian exports to zero", analysts at MUFG said in a note on Wednesday. China has proposed to impose retaliatory tariffs on $60 billion worth of USA goods, including Liquefied Natural Gas (LNG), fueling speculation that it could also impose tariffs on oil.