Note 7 — Debt

Our total debt consisted of the following at March 31, 2016 and December 31, 2015:

	March 31,			December 31,
	2016			2015
Current
Current maturities of long-term debt	$	299,965		$	299,997
Less: Unamortized debt issuance costs		(442	)		(73	)
Current maturities of long-term debt, net of debt issuance costs	$	299,523		$	299,924

Long-term
3.05% Senior Notes due March 2016	$	—		$	299,997
2.50% Senior Notes due March 2017		299,965			299,956
5.00% Senior Notes due March 2018		249,645			249,602
7.50% Senior Notes due March 2019		201,695			201,695
4.90% Senior Notes due August 2020		499,322			499,287
4.625% Senior Notes due March 2021		399,694			399,680
3.95% Senior Notes due March 2022		399,377			399,354
6.95% Senior Notes due April 2025		448,838			448,814
6.20% Senior Notes due August 2040		399,897			399,896
6.05% Senior Notes due March 2041		397,728			397,719
5.25% Senior Notes due March 2042		498,346			498,338
7.95% Senior Notes due April 2045		394,577			394,563
Total senior unsecured notes		4,189,084			4,488,901
Credit facility & commercial paper program		—			—
Total debt		4,189,084			4,488,901
Less: Unamortized debt issuance costs		(25,059	)		(26,266	)
Less: Current maturities of long-term debt		(299,965	)		(299,997	)
Long-term debt, net of debt issuance costs	$	3,864,060		$	4,162,638

In accordance with our adoption of ASU No. 2015-03, unamortized debt issuance costs related to our senior notes are shown as a direct reduction of the carrying amount of the related debt. The debt issuance costs previously included in “Other assets,” are included in either “Current maturities of long-term debt” or “Long-term debt” in the accompanying Consolidated Balance Sheets, based upon the maturity date of the respective senior notes.

Credit Facility and Commercial Paper Program

We currently have a five-year $2.4 billion senior unsecured credit facility that matures in January 2020. The credit facility provides us with the ability to issue up to $500 million in letters of credit. The issuance of letters of credit under the facility reduces the amount available for borrowing. At March 31, 2016, we had no letters of credit issued under the facility.

We also have a commercial paper program that allows us to issue up to $2.4 billion in unsecured commercial paper notes. Amounts issued under the commercial paper program are supported by the unused capacity under our credit facility and, therefore, are classified as long-term on our Consolidated Balance Sheet. The outstanding amounts of commercial paper reduce availability under our credit facility. Access to our commercial paper program is dependent upon our credit ratings. As our credit ratings are below investment grade, we are currently prohibited from accessing the commercial paper market.

As of March 31, 2016, we had no amounts drawn on our credit facility.

Our credit facility and certain of our senior notes, as discussed below, have provisions which vary the applicable interest rates based upon our credit ratings.

Senior Unsecured Notes

In March 2015, our indirect wholly-owned subsidiary, Noble Holding International Limited (“NHIL”), issued $1.1 billion aggregate principal amount of senior notes in three separate tranches, comprised of $250 million of 4.00% Senior Notes due 2018, $450 million of 5.95% Senior Notes due 2025, and $400 million of 6.95% Senior Notes due 2045. The interest rates for these Senior Notes are subject to adjustment from time to time upon a change to our debt rating, pursuant to the terms of these Senior Notes. In February 2016, as a result of a reduction in our debt rating below investment grade, the interest rates on these Senior Notes were increased to 5.00%, 6.95% and 7.95%, respectively, effective the first day of each interest period after which the downgrade occurred. The interest rates on these Senior Notes may be further increased if our debt rating were to be downgraded further (up to a maximum of an additional 100 basis points).

In March 2016, we repaid our $300 million 3.05% Senior Notes using cash on hand.

In March 2016, we commenced cash tender offers for our 4.90% Senior Notes due 2020, of which $500 million principal amount was outstanding, and our 4.625% Senior Notes due 2021, of which $400 million principal amount was outstanding. On April 1, 2016, we purchased $36 million of these Senior Notes using cash on hand.

Our $300 million 2.50% Senior Notes mature during the first quarter of 2017. We anticipate using cash on hand to repay the outstanding balances.

Covenants

The credit facility is guaranteed by NHIL and Noble Holding Corporation (“NHC”). The credit facility contains a covenant that limits our ratio of debt to total tangible capitalization, as defined in the credit facility, to 0.60. At March 31, 2016, our ratio of debt to total tangible capitalization was approximately 0.36. We were in compliance with all covenants under the credit facility as of March 31, 2016.

In addition to the covenants from the credit facility noted above, the indentures governing our outstanding senior unsecured notes contain covenants that place restrictions on certain merger and consolidation transactions, unless we are the surviving entity or the other party assumes the obligations under the indenture, and on the ability to sell or transfer all or substantially all of our assets. In addition, there are restrictions on incurring or assuming certain liens and on entering into sale and lease-back transactions. At March 31, 2016, we were in compliance with all of our debt covenants. We continually monitor compliance with the covenants under our notes and expect to remain in compliance during the remainder of 2016.

Fair Value of Debt

Fair value represents the amount at which an instrument could be exchanged in a current transaction between willing parties. The estimated fair value of our senior notes was based on the quoted market prices for similar issues or on the current rates offered to us for debt of similar remaining maturities (Level 2 measurement). All remaining fair value disclosures are presented in Note 11.

The following table presents the estimated fair value of our total debt, not including the effect of unamortized debt issuance costs, as of March 31, 2016 and December 31, 2015, respectively:

	March 31, 2016				December 31, 2015
	Carrying		Estimated		Carrying		Estimated
	Value		Fair Value		Value		Fair Value
Senior unsecured notes:
3.05% Senior Notes due March 2016	$	—	$	—	$	299,997	$	299,340
2.50% Senior Notes due March 2017		299,965		283,313		299,956		284,334
5.00% Senior Notes due March 2018		249,645		232,369		249,602		227,285
7.50% Senior Notes due March 2019		201,695		172,323		201,695		194,273
4.90% Senior Notes due August 2020		499,322		369,375		499,287		378,761
4.625% Senior Notes due March 2021		399,694		276,500		399,680		289,450
3.95% Senior Notes due March 2022		399,377		242,500		399,354		265,643
6.95% Senior Notes due April 2025		448,838		288,984		448,814		308,870
6.20% Senior Notes due August 2040		399,897		195,500		399,896		237,005
6.05% Senior Notes due March 2041		397,728		195,000		397,719		239,464
5.25% Senior Notes due March 2042		498,346		235,625		498,338		279,919
7.95% Senior Notes due April 2045		394,577		220,500		394,563		255,887
Total senior unsecured notes		4,189,084		2,711,989		4,488,901		3,260,231
Credit facility & commercial paper program		—		—		—		—
Total debt	$	4,189,084	$	2,711,989	$	4,488,901	$	3,260,231