Oil futures were under pressure Monday, pulling back from five-month highs notched last week, after Russia’s finance minister said his country and OPEC may decide to boost output to fight for market share with the U.S.

West Texas Intermediate for May delivery, the U.S. benchmark crude, on the New York Mercantile Exchange CLK9, -0.92%  fell 59 cents, or 0.9%, to $63.30 a barrel. The global benchmark, June Brent crude LCOM9, -0.78% was off 61 cents, or 0.9%, at $70.94 a barrel.

“There is a dilemma. What should we do with OPEC: should we lose the market, which is being occupied by the Americans, or quit the deal?” Russian Finance Minister Anton Siluanov was quoted as saying Saturday by the TASS news agency, according to Reuters. Siluanov said such a move could drive the price of oil to $40 a barrel or below, the report said.

The Organization of the Petroleum Exporting Countries and its allies, primarily Russia, agreed to reduce output by 1.2 million barrels a day for six months beginning Jan. 1. OPEC and its allies are set to meet near the end of June. The reduction in output has been credited with helping to fuel a sharp rally that’s taken WTI, up by around 40% so far this year, while Brent has soared nearly 32%.

Analysts at Commerzbank said a tight global supply situation continues to underpin crude prices — and also appears to be luring in speculators, as reflected by government data showing a continued increase in so-called net long positions held by speculators. Those positions, which are seen as vulnerable to unwinding if prices move sharply against weak-handed traders, hit their highest level since October in the week ended April 9 for both WTI and Brent futures, they said.

Oil futures peaked in October before suffering a brutal fourth-quarter selloff. “No similar slump is likely just now – at least for as long as the oil market remains tight. If this were to change, for example if OPEC decided to expand its supply, and if speculative financial investors closed their net long positions in response, there would be a risk of the price correcting,” the Commerzbank analysts said.

In other energy trade, May gasoline RBK9, -1.18%  fell 2.63 cents, or 1.3%, to $2.0107 a gallon, while May heating oil HOK9, -0.88%  dropped 2.19 cents, or 1.1%, to $2.0488 a gallon.

May natural gas NGK19, -1.28%  fell 2.52 cents, or 1.2%, to $2.0118 per million British thermal units.

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