From the IRS
The IRS released standard mileage rates for use in 2012 (Notice 2012-1). Taxpayers can use the optional standard mileage rates to calculate the deductible costs of operating an automobile.
The rate for business use of an automobile remains at 55½ cents per mile. For medical or moving expenses, it is 23 cents per mile (a ½ cent decrease from the second half of 2011). For services to charitable organizations, the rate (which is set by statute) is 14 cents per mile.
Rather than using the standard mileage rates, taxpayers may instead claim actual costs if they maintain adequate records and can substantiate their expenses. The rules for substantiating these amounts appear in Rev. Proc. 2010-51.
For automobiles a taxpayer uses for business purposes, the portion of the business standard mileage rate treated as depreciation is 23 cents per mile for 2012 (it was 22 cents per mile for 2011).