Oil prices slipped today after China posted its slowest quarterly economic growth in at least 27 years, reinforcing concerns about demand in the world's largest crude oil importer. 

Brent crude futures for September fell 15 cents, or 0.2%, to $66.57 a barrel in early trade while US crude for August was down 24 cents, or 0.4%, at $59.97 a barrel. 

Both contracts last week posted their biggest weekly gains in three weeks on cuts in US oil production and diplomatic tensions in the Middle East. 

Refineries in the path of Tropical Storm Barry continued to operate despite flood threats while the storm has slashed US Gulf of Mexico crude output by 73%, or 1.38 million barrels per day. 

China's economic growth slowed to 6.2% in the second quarter from a year earlier, in line with analysts' expectations, with demand at home and abroad faltering as the Sino-US trade war bites. 

China's crude oil throughput rose to a record of 13.07 million barrels per day in June, up 7.7% from a year earlier, following the start-up of two new, large refineries, official data showed today. 

ANZ analysts said China's crude oil imports year-to-date still looked impressive even as imports fell in June for a second month in a row. 

In the Middle East, Iranian President Hassan Rouhani said in a televised speech on Sunday that Iran is ready to hold talks with the US if Washington lifts sanctions and returns to the 2015 nuclear deal it quit last year.

Meanwhile Britain has offered to facilitate the release of the detained Iranian oil tanker Grace 1 if Tehran gave guarantees that it would not go to Syria.