5.  Long-Term Debt

Our long-term debt was as follows (in thousands):

At March 31, 2015 and December 31, 2014, the balance outstanding of our senior notes, which bear an annual interest rate of 8.50% and mature on June 15, 2019 (the “8.50% Senior Notes”), was classified as long-term at their carrying value.  Interest on the 8.50% Senior Notes is payable semi-annually in arrears on June 15 and December 15.  The estimated annual effective interest rate on the 8.50% Senior Notes is 8.4%, which includes amortization of debt issuance costs and premiums.  We are subject to various financial and other covenants under the indenture governing the 8.50% Senior Notes and we were in compliance with those covenants as of March 31, 2015.  

As of March 31, 2015, the Fifth Amended and Restated Credit Agreement (the “Original Credit Agreement”) governed our revolving bank credit facility and matures on November 8, 2018.  Borrowings under our revolving bank credit facility are secured by our oil and natural gas properties.  Availability under such facility is subject to a semi-annual redetermination of our borrowing base that occurs in the spring and fall of each year and is calculated by our lenders based on their evaluation of our proved reserves and their own internal criteria.  

At both March 31, 2015 and December 31, 2014, we had $0.6 million of letters of credit outstanding under the revolving bank credit facility.  The estimated annual effective interest rate was 3.2% for the three months ended March 31, 2015 for borrowings under the revolving bank credit facility.  The estimated annual effective interest rate includes amortization of debt issuance costs and excludes commitment fees and other costs.  As of March 31, 2015, our borrowing base was $750.0 million and our borrowing availability was $235.4 million.  

In April 2015, we entered into the Amendment to the Original Credit Agreement (collectively, the “Credit Agreement”).  The maturity date of the Original Credit Agreement was not changed by the Amendment and remains at November 8, 2018.  The Amendment lowered the borrowing base to $600.0 million, revised the financial covenant tests and obligated us to certain additional restrictions and conditions.  In addition, the Amendment modified certain financial ratio covenants retroactively to the reporting period for March 31, 2015.  See Note 12 for information on the Amendment, the Credit Agreement and a pending term loan transaction.

Under the Credit Agreement, we are subject to various financial covenants calculated as of the last day of each fiscal quarter, including a minimum current ratio, a maximum leverage ratio, a maximum first lien leverage ratio, a maximum secured debt leverage ratio and a minimum interest coverage ratio.  We were in compliance with all applicable covenants of the Credit Agreement as of March 31, 2015.  

For information about fair value measurements for our 8.50% Senior Notes and revolving bank credit facility, refer to Note 6.