NEW YORK -- U.S. oil futures rose Monday as traders focused on the closure of the Houston Ship Channel and the possibility of more economic sanctions by the West against Russia.

Light, sweet crude for May delivery settled up 14 cents, or 0.1%, at $99.60 a barrel on the New York Mercantile Exchange. U.S. oil futures have risen four of the past five sessions.

Brent crude on ICE Futures Europe shed 11 cents, or 0.1%, to $106.81 a barrel.

The key waterway linking refineries and petrochemical plants with the Gulf of Mexico remained closed indefinitely to ship traffic Monday, two days after a collision between a barge and a bulk carrier caused an estimated 4,000 barrels of fuel oil to spill into Galveston Bay. Eighty-one ships were waiting Monday to enter the Houston Ship Channel, according to the U.S. Coast Guard.

The uncertainty of when the channel would reopen buoyed oil prices, as did tensions over Russia's annexation of the Crimea region. The Wall Street Journal on Monday reported White House officials have indicated President Barack Obama will press U.S. allies to adopt more sweeping sanctions and suspend Russia from the Group of Eight leading nations.

However, some market watchers said oil prices won't rally unless the sanctions specifically target Russia's energy sector.

"Barring an actual disruption of oil and gas exports from Russia, we see downside risk for both WTI [West Texas Intermediate] and Brent crude oil," energy markets strategist Tim Evans at Citi Futures says in a note, pointing to a potential global supply surplus in the second quarter.

A sharp slowdown reported in China's manufacturing activity had some traders selling futures in anticipation of lower oil demand there, while others bought on hopes that China's leaders would respond to the report and other recent disappointing data by ramping up spending.

"It is a mix of both bullish and bearish forces that will keep this market pushing and pulling this week at around the $100 mark," said Jim Ritterbusch, president of Ritterbusch & Associates.

Reformulated gasoline blendstock, or RBOB, for April delivery settled down 1.7 cents, or 0.6%, to $2.8909 a gallon. April diesel settled down 0.85 cents, or 0.3%, at $2.9116 a gallon.