Your response to my request for clarification is a little unclear, but I am assuming that you are talking about mileage for a job that you get a W-2 for, and therefore you are entering the mileage in the Job-Related Expenses topic. After you enter your mileage, continue through the questions about other job-related expenses. After all the questions about various kinds of expenses, you will get to a screen that asks whether you received any reimbursements for your expenses. Select Yes, then enter the amount that the employer paid for gas as a reimbursement.
