The world’s largest drilling company Boart Longyear says it will reduce the size of its revolving credit facility from $US450 million to $US140 million.

The company said the change was subject to its completion of a $US300 million debt offering.

It comes a week after ratings agency Standard and Poor’s cut the company’s credit rating from B+ to B, and revised its ratings outlook from stable to negative.

Boart recently recorded a loss of $US329 million ($A366.13 million) for the first half of 2013, driven largely by massive falls in earnings in its drilling services division as mining companies continue to slash their exploration budgets.

Shares in the company dropped 3.5 cents, or 7.1 per cent, to 45.5 cents.