Separately, a Reuters poll indicated total US crude inventories may have fallen last week.

Brent crude settled up $1.38, or 2.9%, at $48.35 per barrel. Minutes after the close, it extended gains, reaching $48.46, its highest since 12 July.

Brent has gained about 10% cumulatively in the past three sessions, its most in such a stretch since May. Since the start of August, it has risen nearly 14%.

US West Texas Intermediate (WTI) crude rose $1.25, or 2.8%, to settle at $45.74 per barrel. It also rallied post-settlement to $45.87, its highest since 21 July. WTI has gained 10% on the month.

Russian Energy Minister Alexander Novak bolstered hopes on Monday that oil-producing nations could take action to stabilise prices.

The market started to rally on Thursday after Saudi Arabia's Energy Minister Khalid al-Falih said non-members and members of Opec are to meet on the sidelines of the International Energy Forum in Algeria from 26 to 28 September.

"While we see very little possibility of an actualisation of curtailed Opec output, there will likely be enough chatter during the next five to six weeks to deter selling in allowing WTI to gravitate at around the $45 area, at least through the second half of this month," said Jim Ritterbusch of Chicago-based oil markets consultancy Ritterbusch & Associates.

Other analysts were sceptical that the rally would continue.

"In our view, a renewed price correction cannot be ruled out if market participants start focusing on the supply side again, for the latest drilling activity figures in the US cast doubts that the oversupply is really being eroded," Commerzbank analyst Carsten Fritsch said in a note.

There are also doubts that Saudi Arabia and other major Opec members such as Iran will put aside a market share battle in order to prop up prices.

New York-based crude cargo tracker Clipperdata said exports by Opec's big six - Saudi Arabia, Iran, Kuwait, Qatar, Iraq and the United Arab Emirates - total 3.3 million barrels per day, or nearly 22%, more from their 2015 start of 18.5 million bpd.

"It seems prudent to point out the contrast betwixt actions versus words," said Clipperdata analyst Matt Smith said, referring to Opec.

On the demand side, the world's three biggest economies - the US, China and Japan - all published downbeat economic data between Friday and Monday that could spell erosion in oil demand.