In short, because there are a lot of tricky steps to get oil from inside the Earth to inside, say, your gas tank:
1. oil spills can be caused by the accidental or intentional release of any form of petroleum during any point in the oil production process, from drilling, refining, or storing to transporting.
2. Oil can be spilled when a pipeline breaks, ships collide or are grounded (as happened earlier along the Great Barrier Reef), underground storage tanks leak, or in the current case, when an oil rig explodes or is damaged.
3. AND oil spills can also happen naturally when oil is released into the ocean from natural oil seeps on the seafloor.
Machinery breaks down folks. That’s why it’s a depreciative item.