Exxon and Chevron leaned on strong performances from their refining operations to increase profits in the third quarter despite plummeting global oil prices. [...] low oil and natural gas prices make for low raw material costs — and higher profit — for refining and chemical operations, which turn oil and gas into fuels and chemicals. The trend lately has been for integrated oil and gas companies, which own production, refining and distribution assets, to spin off their refining operations into different companies in an effort to better appeal to investors. [...] other major oil international oil companies, such as BP, ConocoPhillips and Total, saw earnings fall in the third quarter on lower oil prices. [...] a reason oil prices have fallen so far is that demand for fuels is weakening around the world, which could limit output and profit gains at refining operations.