"n brief, because there are a lot of tricky steps to get oil from inside the Earth to inside, say, your gas tank. 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. Oil can be spilled when a pipeline breaks, ships collide or are grounded (as happened earlier this month along the Great Barrier Reef), underground storage tanks leak, or in the current case, when an oil rig explodes or is damaged. IN PICTURES: Big Environmental Disasters Some oil was spilled when the Deepwater Horizon rig first burst into flames on April 20 in the Gulf, injuring crew members and sending a billowing plume of black smoke into the sky that could be seen by satellite. The oil rig, located about 51 miles (82 kilometers) southeast of Venice, La., then sank into the Gulf waters Thursday morning, creating concern that more oil could spill. Oil spills can also happen naturally: Oil is released into the ocean from natural oil seeps on the seafloor. The best known such seep is Coal Oil Point along the California coast where an estimated 2,000 to 3,000 gallons (7,570 to 11,400 liters) of crude oil is released each day."