An investigation on the flaring and venting of natural gas by fossil fuel companies in more than a dozen states across the country.

A four-part series by the Howard Center for Investigative Journalism at Arizona State’s Walter Cronkite School of Journalism and Mass Communication finds that over much of the last decade, oil and gas operators in 13 U.S. states have flared, or burned off, at least 3.5 trillion cubic feet of natural gas. That’s equivalent to the greenhouse gas emissions of nearly 42 million cars driving for a year.