Crude futures aimed lower Tuesday after exchange-operator CME Group Inc. (CME) raised margins on its U.S. benchmark oil-futures contracts.

Gasoline futures continued climbing, however, as investors worry that flooding of the Mississippi River and its tributaries could force refineries in the region to halt production of fuel products.

Light, sweet crude for June delivery recently traded $1.50, or 1.4%, lower at $101.05 a barrel on the New York Mercantile Exchange. Brent crude on the ICE futures exchange traded 97 cents lower at $114.93 a barrel.

Oil prices slumped after CME raised maintenance margins on crude to $6,250 a contract from $5,000 a contract, making it more expensive for speculators and other market participants to hold on to positions.

The margin increase "would be a reason for a little bit of the give back," said Matt Smith, an oil analyst with Summit Energy. He said the market is likely consolidating around the $100-a-barrel level, as "people are tentative to jump back in fully," after the massive swings last week and on Monday.

While crude prices look for direction, gasoline continues to march higher on worries that refineries in Louisiana will be forced to shut down as floodwaters inundate the region.

Front-month June reformulated gasoline blendstock, or RBOB, recently traded 2.45 cents, or 0.8%, higher at $3.3029 a gallon.

"Heavy floods in the U.S...could impact numerous refineries, as well as deliveries of crude and products in the region," said JP Morgan analysts in a research report. "Although the situation still remains uncertain, refineries, terminals, and other oil infrastructure are expected to take proactive measures to ensure safety, potentially reducing runs or shutting facilities if necessary."

U.S. gasoline stockpiles have fallen for 11-straight weeks, and analysts surveyed by Dow Jones Newswires expect further declines when data is released by the Energy Department on Wednesday. The situation could help push average U.S. retail gasoline prices above the $4 a gallon level, straining the budgets of consumers and businesses and potentially weighing on the economic recovery.

Crude inventories are expected to rise by 1.1 million barrels, according to the survey. Gasoline stockpiles are expected to fall by 200,000 barrels. Stockpiles of distillates, which include heating oil and diesel, are seen rising by 700,000 barrels.

Gasoline has been an important driver of crude prices in recent weeks, as investors try to gauge whether high prices at the pump will crimp demand for oil.

Oil futures are attempting to establish some stability after the massive plunge last week and Monday's dramatic recovery. But analysts caution that more swings could be ahead until investors are more confident that the market is on firmer footing.

"We would not be surprised to see daily moves of $3 to $5 a day in either direction at least until the dust settles slightly," Ed Meir, commodities analyst at MF Global, said in a client note.

June heating oil recently traded 2.92 cents lower at $2.9326 a gallon.