The cost of gas is going up again but the IRS has not updated the 2012 mileage rates to reflect the increased price.  Effective January 1, 2012, the standard mileage rates for the use of a car (also vans, pickups or panel trucks) will be:

55.5 cents per mile for business miles driven
23 cents per mile driven for medical or moving purposes
14 cents per mile driven in service of charitable organizations

The rate for business miles driven is unchanged from the mid-year adjustment that became effective on July 1, 2011. The medical and moving rate has been reduced by 0.5 cents per mile.

Acording to the IRS, taxpayers always have the option of calculating the actual costs of using their vehicle rather than using the standard mileage rates. A taxpayer may not use the business standard mileage rate for a vehicle after using any depreciation method under the Modified Accelerated Cost Recovery System (MACRS) or after claiming a Section 179 deduction for that vehicle. In addition, the business standard mileage rate cannot be used for more than four vehicles used simultaneously. These and other requirements for a taxpayer to use a standard mileage rate to calculate the amount of a deductible business, moving, medical or charitable expense are in Rev. Proc. 2010-51.

Notice 2012-01 contains the standard mileage rates, the amount a taxpayer must use in calculating reductions to basis for depreciation taken under the business standard mileage rate, and the maximum standard automobile cost that a taxpayer may use in computing the allowance under a fixed and variable rate plan.

Additional information can be found at http://www.irs.gov/newsroom/article/0,,id=250882,00.html