National gas prices are soaring again — this time by 5.31 cents per gallon in the past two weeks — to $3.18, according a survey by analyst Trilby Lundberg.

The increase mirrors a leap in crude-oil prices, which have been under upward pressure due to continued unrest in the Arab states. Futures gained as much as 1.2 percent yesterday after security forces in Libya launched attacks on anti-government protesters. Trading is closed today for the Presidents Day holiday.

The average price for mid-grade was $3.32, and premium was at $3.43. Diesel was up nine cents, to $3.59 a gallon.

Billings, Mont., had the lowest average price among cities surveyed at $2.95 a gallon for regular, while San Francisco is the highest at $3.54.