As economic growth outside the US has flagged, producers and traders are beginning to worry that demand for crude will also decline
For the month, Brent futures are set to drop 6.2 per cent, the most since July 2016
A sharp drop in crude oil prices have helped improved investor sentiment
OPEC, together with some non-OPEC producers including Russia started withholding output in 2017 to end a global supply overhang and prop up prices
The largest US refinery, Motiva Enterprises' 603,000 bpd Port Arthur facility in Texas, began a planned one-month overhaul on Monday of its key crude oil processing unit.
Brent crude, the international benchmark for oil prices, slipped 15 cents to $65.10 a barrel at 1153 GMT