Official site for W-2, W-3 forms: http://www.ssa.gov/employer/
prayers
Taxable Income by: Vickey
If you are just issuing him a check for a gas allowance and it is not through a properly set up accountable reimbursement plan, then yes...it would be included in box 1 of his W-2. He won’t owe any SS tax because of his opting out, but he will owe income tax on it.
Gas allowance by: Anonymous
It depends on how you pay it, check out IRS pub 15B http://www.irs.gov/pub/irs-pdf/p15b.pdf and also https://www.freechurchaccounting.com/accountablereimbursementpolicy.html