A gas leak from the underground Aliso Canyon gas storage started in October 2015 releasing methane in an uncontrolled fashion . By December 2015 , thousands of people from Porter Ranch had been temporarily relocated and the leak had added more than 150 million pounds of methane to the atmosphere . The NGO Environmental Defense Fund has called the incident " unprecedented for California " and compared the leak 's continuous output of greenhouse gas emissions to that of 7 million cars or " 8 or 9 coal-fired plants " . The 20-year climate impact of this leak is estimated to be the same as burning a billion gallons of gasoline . The incident has been called " the biggest environmental disaster since the Deepwater Horizon oil spill " by journalists
Deepwater Horizon oil spill
Deepwater Horizon oil spill
Southern California Gas Company