Brent crude futures slipped 36 cents to $56.58 a barrel, while the US West Texas Intermediate (WTI) crude futures were down by 32 cents to $50.98 reported Reuters. Prices are up 4.4 percent this week.
Chinese oil demand is on track to rise by 820,000 barrels a day this year, according to Jefferies Group LLC.
Global oil stockpiles will fall this year by 300,000 barrels a day as stronger demand and output curbs by OPEC and Russian Federation whittle away a surplus, the IEA said Thursday in its monthly report.
Prices also gained amid tensions in Iraq between the central government and the country's semi-autonomous Kurdish region.
Local media in the country is reporting that tens of thousands of Kurds have turned out to fight Iraqi forces in the oil rich Kirkuk region.
The step would give the U.S. Congress 60 days to decide whether to impose sanctions, but Iran's parliament speaker told the TASS news agency that decertification would "be the end" of the deal and cause "global chaos".
President Donald Trump is expected to reveal in a speech Friday afternoon whether he will certify a 2015 global agreement with Iran to curb the Islamic Republic's nuclear program in exchange for economic sanctions relief.
Angola's production, based on direct communication, was 1.657 million barrels per day, a monthly drop of 23,000 barrels, with no data from Nigeria in this case.
Separately, Saudi Aramco said it was considering shelving plans for an worldwide public offering (IPO) in favour of a private share sale to world sovereign funds and institutional investors, the Financial Times reported, citing people familiar with the matter.
Traders said they would look to USA fuel inventory data on Wednesday and Thursday for indicators on price direction.
"(Saudi Arabia) may need oil prices to go even higher if the IPO does not go through", Flynn said.