Crude settled lower on Monday, as investors questioned whether OPEC would seek to extend the current deal to curb global supply amid rising levels of U.S. production.
On the New York Mercantile Exchange crude futures for June delivery shed 39 cents to settle at $49.23 a barrel, while on London's Intercontinental Exchange, Brent traded at $52.16 a barrel, down 28 cents.
Oil prices fell for a sixth day, as focused shifted to the ramp-up of U.S. drilling activity ahead of a report on inventories from the Energy Information Administration on Wednesday.
Oilfield services firm Baker Hughes reported Friday, its weekly U.S. rig count rose by 5 to 688, which fuelled fears that rising U.S. shale production could weigh on efforts by OPEC and other major producers to curb the glut in supply.
The rise in U.S. drilling activity did little to ease concerns that shale production was set for its biggest monthly increase in more than two years.
Meanwhile, investors began to question whether OPEC would seek to extend the current deal to cut global supply amid a lack of confirmation from the oil cartel.
Elsewhere, Russian Energy minister Alexander Novak said Friday, "There are no decisions yet [concerning an extension to the deal to cut supply] and each country is currently studying this issue independently,"
OPEC has previously reiterated that Russia and non-members would need to remain part of the initiative to cut supply.
OPEC will decide at talks on May 25 whether to extend production cuts beyond June.
In November last year, OPEC and other producers, including Russia agreed to cut output by about 1.8 million barrels per day (bpd). The deal to cut supply came into effect in January this year for a period of six-months until June.