The correct answer is B) increase. As the temperature of a fuel oil stored in a tank rises, the volume of the fuel oil will increase. This is due to the principle of thermal expansion, which states that as the temperature of a substance increases, its volume also increases. This is a fundamental property of liquids, including fuel oils. The increase in volume is caused by the increased kinetic energy of the fuel oil molecules, which causes them to spread out and occupy a larger volume. The other answer choices are incorrect because a decrease in volume (A) would contradict the principle of thermal expansion, and the volume remaining the same (C) would also be inconsistent with the physical behavior of liquids when heated.