Top global miner BHP Billiton (LON:BLT) has announced that it will book a $7.2 billion writedown on the value of its U.S. shale assets, after plummeting commodity prices led to a sharp slump in 2015 earnings.

BHP Billiton Chief Executive Officer, Andrew Mackenzie, said:

“Oil and gas markets have been significantly weaker than the industry expected. We responded quickly by dramatically cutting our operating and capital costs, and reducing the number of operated rigs in the Onshore US business from 26 a year ago to five by the end of the current quarter.

“While we have made significant progress, the dramatic fall in prices has led to the disappointing write down announced today. However, we remain confident in the long-term outlook and the quality of our acreage. We are well positioned to respond to a recovery.”

A slump in oil prices by 70 percent over the last year has led to difficulties for all commodities companies. Ratings agencies Moody’s and Standard & Poor’s have both warned that the BHP Billiton’s dividend policy poses a risk to its credit rating.

BHP saw a sharp drop in share price on the news, currently trading down 5.49 percent at 620.90 pence per share (1043GMT).

15/01/2016