If the tanker is driven by a civilian and we bomb it, guess what? We killed a civilian, which is a war crime.
Before we bombed cities in WW2, we dropped leaflets asking civilians to evacuate. During Operation Rolling Thunder, we dropped leaflets asking civilians to evacuate. Before Fallujah, we dropped leaflets asking civilians to evacuate. It's called Rules of Engagement and the Laws of War. As soon as we don't play by them, that means in the future any country that goes to war with us doesn't have to play by them. If we do play by them, any other country we go to war with in the future will most likely play by them. I'll hedge my bets towards the option that's the safest towards our servicemen.