Debt

Total debt, including the current portion of long-term debt, consisted of the following:



(millions)	September 30, 2013		December 31, 2012
6.3% senior notes due 2016	$	500	$	500
7.75% senior notes due 2018, net of discount	500		499
7.875% senior notes due 2020, net of discount	249		248
8.375% senior notes due 2018	350		350
9.75% senior notes due 2014, net of discount	59		59
10% convertible senior notes due 2018, net of discount	386		385
Ship mortgage facility (includes $4 million of current portion of long-term debt)	25		29
Credit facilities of Oman joint ventures	7		—
Industrial revenue bonds (due 2028 through 2034)	239		239
Total	$	2,315	$	2,309

U.S. Credit Facility: Our U.S. credit facility contains a single financial covenant that would require us to maintain a minimum fixed charge coverage ratio of no less than 1.1-to-1.0 if and for so long as the excess of the borrowing base over the outstanding borrowings under the credit agreement is less than the greater of (a) $40 million and (b) 15% of the lesser of (i) the aggregate revolving commitments at such time and (ii) the borrowing base at such time. As of September 30, 2013, our fixed charge coverage ratio was 0.97-to-1.0. Because we do not currently satisfy the required fixed charge coverage ratio, we must maintain borrowing availability of at least $52 million under the credit facility. Taking into account the most recent borrowing base calculation delivered under the credit facility, which reflects trade receivables and inventory as of September 30, 2013, outstanding letters of credit of $78 million as of September 30, 2013 and the current borrowing availability requirement of $52 million, borrowings available under the credit facility were approximately $216 million. As of September 30, 2013 and during the quarter then-ended, there were no borrowings under the facility.

CGC Credit Facility: As of September 30, 2013 and during the quarter then-ended, there were no borrowings outstanding under our Canadian credit agreement. The U.S. dollar equivalent of borrowings available under this agreement as of September 30, 2013 was $38 million.

Oman Credit Facilities: In June 2013, our joint ventures in Oman, which are fully consolidated, each entered into separate secured credit agreements, which are guaranteed by us and our joint venture partner. The credit agreement for Zawawi Gypsum LLC, or ZGL, which matures in 2020, provides for term loans not to exceed $10 million and overdraft and letter of credit facilities of approximately $3 million in the aggregate. The credit agreement for USG-Zawawi Drywall LLC, or ZDL, which matures in 2022, provides for term loans not to exceed $26 million and overdraft and letter of credit facilities of $5 million in the aggregate. Each credit agreement is secured by a general security interest in the applicable joint venture's assets. Loans under the credit agreements may be made in Omani Rial or U.S. dollars. Loans made in Omani Rial bear interest at 4% and loans made in U.S. dollars bear interest at a floating rate based on the London Interbank Offering Rate, or LIBOR, plus 3.5%. Loans may be repaid at any time, subject to a prepayment penalty if repaid within the first two years, for ZGL, or three years, for ZDL. As of September 30, 2013, there was $7 million in outstanding term loan borrowings under the ZGL credit agreement with an average effective interest rate of 3.8% and no term loan borrowings under the ZDL credit agreement.

The credit agreements for each of the foregoing credit facilities contain customary covenants that may limit us or our joint ventures from taking certain actions. Borrowings under these credit agreements are subject to acceleration upon the occurrence of an event of default.

The fair value of our debt was approximately $3.093 billion as of September 30, 2013 and December 31, 2012. The fair value was based on quoted market prices of our debt or, where quoted market prices were not available, on quoted market prices of instruments with similar terms and maturities or internal valuation models and as a result are classified as Level 2. See Note 9 for further discussion on fair value measurements and classifications.

As of September 30, 2013, we were in compliance with the covenants contained in our credit facilities.

See Note 19 for a discussion of certain debt financing related to our October 2013 announcement of the USG Boral Joint Venture (as defined below).