Alpha Natural Resources Inc. filed for bankruptcy, becoming the latest victim of the coal industry’s worst downturn in decades.

The second-largest U.S. coal producer has lost almost all its market value since 2011, when it bought Massey Energy Co. for about $7 billion. The deal made it the biggest U.S. producer of metallurgical coal, used in steelmaking — and steeped it in debt — right before prices nosedived.

In July, the Bristol, Virginia-based company said it had drawn $445 million from a revolving loan, mostly to fund its business, and it warned investors that it won’t pay $109 million on notes due Aug. 1. Alpha said in a statement Monday that it had secured $692 million in bankruptcy financing, arranged by Citigroup Inc.

U.S. coal companies invested billions of dollars to expand their reserves in 2011 as prices for “met” coal went as high as $330 a metric ton. Then demand from China suddenly slowed and the price of natural gas dropped, cutting into their business. A strong dollar has also kept exports in check.

Details emerging ahead of the release of President Barack Obama’s Clean Power Plan show pressure from Washington to curb coal’s use will only intensify over the next 15 years, escalating the industry’s fight for survival.