International benchmark Brent crude fell to $69.59 per barrel at 11.45 GMT on Friday, while the American benchmark West Texas Intermediate (WTI) saw prices drop to $59.63 per barrel.
Brent crude started trading at $72.62 per barrel at 0642 GMT on Monday, while WTI saw prices of $62.86 per barrel.
The Energy Information Administration (EIA) said Wednesday that inventories of crude oil in the U.S. surged by 5.8 million barrels last week to 432 million barrels, the highest since early June.
According to the EIA's data, U.S. oil production reached a record 11.6 million barrels a day last week from 11.2 million barrels during the week before.
Meanwhile, the second wave of renewed U.S. sanctions on OPEC's third largest exporter, Iran, officially started on Monday targeting Iran's energy, shipbuilding, shipping, and financial sectors.
Experts agreed that the downward price trend would remain amid concerns of a global economic slowdown and market oversupply.
By Gulsen Cagatay