Employers may need to adjust their mileage reimbursements to employees. The Internal Revenue Service (IRS) has announced an increase in the optional standard mileage rates for the final six months of 2011. The rate will increase to 55.5 cents a mile for all business miles driven from July 1, 2011, through Dec. 31, 2011. This is an increase of 4.5 cents from the 51 cent rate in effect for the first six months of 2011. The IRS announced that it made this special adjustment in recognition of recent gasoline price increases. The IRS normally updates the mileage rates once a year in the fall for the next calendar year.