Gasoline reimbursements must be declared as income if they appear in a W-2 form, according to Zacks Investment Research. Such reimbursements, however, should not be included as part of income if they are part of an employer's accountable plan and do not appear in a W-2 form.
If the gas reimbursement appears on the W-2, the amount must be added to the wages, salaries and tips line on Form 1040 when preparing the year's taxes, reports Zacks Investment Research. This means that a taxpayer pays taxes on this as income, although such reimbursements can also be counted as a deduction afterward. Reimbursements that are part of accountable plans commonly have to be accounted for in expense reports, and any extra funds have to be returned.