Warren Resources Inc.has decided not to make a $7.5 million semi-annual interest payment that was due Monday on its 9% senior unsecured notes. The company said it has sufficient liquidity to pay the $300 million notes, of which $167.3 million is outstanding and due by 2022, but is restructuring its balance sheet. Failure to pay the interest does not result in default, Warren said, but if the payment is not made within 30 days the company would default. In that event, Warren would also default under its first and second lien credit facilities. The company has hired Jefferies LLC as a financial adviser to help with the balance sheet restructuring.