They are, for the most part, making roughly the same percentage of profit as the majority of other fortune 500 companies. Ever heard the saying it takes money to make money? Well someone with $1 million invested at a rate of 5% returns will make $50,000 in a given time period, while someone with only $100,000 will only make $5,000.
Big oil companies are making the same percentage of money as everyone else, but since their profit is numerically much larger than other companies, people say they "are making more profit than ever."
They put in billions of dollars for R&D, manufacturing, processing, transporting, etc. Mom and pop's ice cream shop might put in $10,000. Now, if mom and pop's ice cream shop profits $5,000, they saw profits of 50%. If Exxon-Mobil, who put in say $10billion saw 50% returns, they would get back $5 billion in profits. Who's to say they shouldn't reap the same rewards that mom and pop does?