2.Long-Term Debt

Debt at March 31, 2016 and December 31, 2015 consisted of the following:


	March 31, 2016				December 31, 2015
			Unamortized Debt				Unamortized Debt
(in thousands)	Principal		Issuance Costs		Principal		Issuance Costs
5.875% Senior Notes, due May 1, 2022	$	750,000	$	6,649	$	750,000	$	6,978
4.375% Senior Notes, due June 1, 2024		750,000		7,140		750,000		7,402
Total long-term debt	$	1,500,000	$	13,789	$	1,500,000	$	14,380

All of our long-term debt is senior unsecured debt and is, therefore, pari passu with other unsecured debt with respect to the payment of both principal and interest.

Bank Debt

We have a senior unsecured revolving credit facility (Credit Facility) that matures October 16, 2020. The Credit Facility has aggregate commitments of $1.0 billion, with our option to increase aggregate commitments to $1.25 billion at any time. There is no borrowing base subject to the discretion of the lenders based on the value of our proved reserves under the Credit Facility. As of March 31, 2016, there were no borrowings outstanding under the Credit Facility. We had letters of credit outstanding under the Credit Facility of $2.5 million, leaving an unused borrowing availability of $997.5 million.

At our option, borrowings under the Credit Facility may bear interest at either (a) LIBOR plus 1.125 – 2.0% based on the credit rating for our senior unsecured long-term debt, or (b) a base rate (as defined in the credit agreement) plus 0.125 – 1.0%, based on the credit rating for our senior unsecured long-term debt. Unused borrowings are subject to a commitment fee of 0.125 – 0.35%, based on the credit rating for our senior unsecured long-term debt.

The Credit Facility contains representations, warranties, covenants and events of default that are customary for investment grade, senior unsecured bank credit agreements, including a financial covenant for the maintenance of a total debt-to-capital ratio of no greater than 65%. As of March 31, 2016, we were in compliance with all of the financial and non-financial covenants.

At March 31, 2016 and December 31, 2015, we had $5.4 million and $5.7 million, respectively, of unamortized debt issuance costs associated with our Credit Facility, which were recorded as deferred assets and included in Other assets, net in our balance sheet. These costs are being amortized to interest expense ratably over the life of the Credit Facility.

Senior Notes

Each of our senior notes is governed by an indenture containing certain covenants, events of default and other restrictive provisions with which we were in compliance as of March 31, 2016. Interest on each of the senior notes is payable semi-annually. The effective interest rate on the 4.375% notes and the 5.875% notes, including the debt issuance cost, is 4.50% and 6.04%, respectively.