Oil prices fell on Monday as rising stockpiles of crude and refined fuel intensified fears that another major glut is building.
Market intelligence firm Genscape reported that the Cushing, Oklahoma delivery hub for U.S. crude futures saw a supply build of 26,460 barrels in the week to July 15, traders who saw the data said.
Morgan Stanley said in a report that demand for fuels such as diesel and gasoline were lagging petrochemicals, clouding the outlook for oil.
"A rapid rise of non-petroleum products (demand) is boosting total product demand, but this is unhelpful for crude oil. Based on the latest data, even our tepid 800,000 barrels per day growth estimate for global crude runs looks too high," it said.
U.S. gasoline and distillate stocks surged unexpectedly last week, government data showed, crimping margins for refiners at the height of summer driving season when demand for fuels were generally healthy.
Morgan Stanley said it still expected a supply-demand rebalancing in oil by mid-2017 but added that fundamental headwinds were growing the market. "Tail risks are admittedly large in both directions, as geopolitics add to uncertainty."
Brent crude futures fell 60 cents, or 1.26 percent, at $47.01 a barrel, having gained nearly 2 percent last week.
U.S. crude futures settled down 71 cents, or 1.6 percent, at $45.24 a barrel, and last traded down 1.46 percent at $45.28.
"We are maintaining a bearish trading stance as we still see an ultimate price downdraft in WTI and Brent to about $37 and $38 areas respectively," said Jim Ritterbusch of Chicago-based oil markets consultancy Ritterbusch & Associates.
Turkey's attempted coup barely affected the market as Istanbul's Bosphorus Strait, which handles about 3 percent of global oil shipments mainly from Black Sea ports and the Caspian region, reopened from a brief closure.
Oil prices are up nearly 75 percent since hitting 12-year lows of around $27 for Brent and about $26 for U.S. crude in the first quarter. The rally has stalled since the two benchmarks breached the $50 a barrel mark in May as worries grew that higher prices will fuel more production.
News that oil guards protesting over pay shut Libya's Hariga oil terminal on Sunday dampened hopes the country could boost its output significantly any time soon.
"Libya remains a wild card in the global oil market balance," SEB chief commodities analyst Bjarne Schieldrop said, adding "an immediate revival in Libyan crude exports looks less daunting and might help to support crude prices slightly."
Saudi Arabia's energy minister said on Sunday the kingdom always reacts to oil market supply and demand and would continue to monitor crude markets for any developments.
The race among oil suppliers to meet the rise in demand for imports from China's independent refineries is heating up, with Iran supplying a 2-million-barrel cargo via trader Trafigura.
Oil market investors again cut their bullish bets on Brent to their lowest since February.
Data from the InterContinental Exchange on Monday showed investors cut net long positions by 8,899 to 303,371 in the week to July 12, their lowest since Feb. 22.