Can I deduct mileage if my boss reimburses me for gas only?

I'm an independent contractor for a website, and travel frequently (4,000 miles this year for business). My boss re-pays me for gas costs at the end of each month, but does not re-imburse me for mileage at 55 cents a mile. My boss also just puts the gas repayment on my months' check. Can I still deduct mileage?