I'll address your last comment first. You won't be able to deduct your business mileage on your personal tax return in 2018. TheTax Cuts and Jobs Act of 2017 (TCJA) eliminated the deduction for unreimbursed business expenses. If you are only using the vehicle for business, using the company card for gas is acceptable. A preferable way to handle it would be to submit your mileage and be reimbursed by the company for your mileage.
