Oil prices fell Monday as Tropical Storm Isaac threatened oil and gas operations in the US Gulf of Mexico, forcing refinery shutdowns that lowered demand for crude.

The price of West Texas Intermediate (WTI) light sweet crude for October delivery closed at $95.47 a barrel, down 68 cents from Friday’s close and reversing earlier, much sharper gains.

London’s financial markets were closed for a public holiday, but in electronic trading Brent North Sea crude for delivery in October slumped $1.25 to settle at $112.26 a barrel.

Crude futures prices earlier had been boosted by the shutdown and evacuation of personnel from oil rigs in the US Gulf of Mexico. But as Isaac drew closer to the heart of the US oil industry, market worries eased about its impact.

Concerns over the storm are “fading,” said John Kilduff, an analyst at Again Capital.

“It is not big enough to cause major damage to the energy infrastructure,” Kilduff said.