It is a reaction that produces heat, such as the combustion of fuel in your car, but it is not the same as saying that it releases more energy than it took to make it. There is nothing that produces more energy than it took to produce it in the first place. It took more energy to pump the petroleum out of the ground, refine it, transport it to the station for you to buy, than it did to burn the fuel in your car. It's just that the oil companies make sure that they get enough money in return to offset their expenditures. There is never a net gain in energy if you look at the entire process of what it took to cause the reaction in the first place.