Exxon had a net profit in 2018 of $20.8 billion. So, 20.8 B dollars divided by 34.7 billion gallons they produced is about $.60 per gallon. Note that many of their products are much more valuable than gasoline and we will find that they probably made less than 20 cents per gallon of gas. That is less than 10%. Not much of a profit margin for a very risky business.
Exxon makes about .13 cents a gallon of gas, the US Government taxes it at 18.4 cents a gallon. In Ohio we tax it 38.5 cents a gallon. Our roads should be paved with gold!