The Internal Revenue Service lets you deduct qualified business-related expenses. Auto-related costs fall under this category as long as they meet the IRS criteria. You can track your mileage and deduct the standard amount – which was 56 cents per mile in the 2014 tax year. If you itemize individual car expenses, you can subtract the cost of gas, but only for work-related expenses.
As an Employee
The IRS classifies business expenses as those that occurred over the previous year, were trade or business related and were both “ordinary and necessary.” Despite the “ordinary” label, the cost of buying gas to commute from your home to your office is not deductible. You can, however, deduct the cost of gas from your travel from one business location to another, or for travel to customer sites -- as long as you are not reimbursed by your employer. Business expenses must be greater than 2 percent of your adjusted gross income, and you can only deduct the expenses over that amount. You also can only deduct unreimbursed business expenses. If your employer repaid you for the amount you spent on gas, you can't take the deduction.
If you own your own business, gas used for business travel gets deducted from your business income on your Schedule C. You don’t need to exceed the 2 percent AGI threshold for this. Instead, each dollar of expenses reduces your income subject to taxation. You also have the option of taking the standard mileage deduction instead.