The components of long-term debt (net of discounts), along with maturity dates for the years subsequent to May 31, 2011, are as follows (in millions):

		May 31,
		2011		2010
Senior unsecured debt
	Interest rate of 7.25%, due in 2011	$	-	$	250
	Interest rate of 9.65%, due in 2013		300		300
	Interest rate of 7.38%, due in 2014		250		250
	Interest rate of 8.00%, due in 2019		750		750
	Interest rate of 7.60%, due in 2098		239		239
			1,539		1,789
Capital lease obligations			146		141
			1,685		1,930
	Less current portion		18		262
		$	1,667	$	1,668

Interest on our fixed-rate notes is paid semi-annually. Long-term debt, exclusive of capital leases, had carrying values of $1.5 billion compared with estimated fair values of $1.9 billion at May 31, 2011, and $1.8 billion compared with estimated fair values of $2.1 billion at May 31, 2010. The estimated fair values were determined based on quoted market prices or on the current rates offered for debt with similar terms and maturities.

We have a shelf registration statement filed with the Securities and Exchange Commission that allows us to sell, in one or more future offerings, any combination of our unsecured debt securities and common stock.

During 2011, we repaid our $250 million 7.25% unsecured notes that matured on February 15, 2011. During 2010, we repaid our $500 million 5.50% notes that matured on August 15, 2009 using cash from operations and a portion of the proceeds of our January 2009 $1 billion senior unsecured debt offering. During 2011, we made principal payments in the amount of $12 million related to capital lease obligations. During 2010, we made principal payments in the amount of $153 million related to capital lease obligations.

A $1 billion revolving credit facility is available to finance our operations and other cash flow needs and to provide support for the issuance of commercial paper. This five-year credit agreement was entered into on April 26, 2011, and replaced the $1 billion three-year credit agreement dated July 22, 2009. The agreement contains a financial covenant, which requires us to maintain a leverage ratio of adjusted debt (long-term debt, including the current portion of such debt, plus six times our last four fiscal quarters' rentals and landing fees) to capital (adjusted debt plus total common stockholders' investment) that does not exceed 0.7 to 1.0. Our leverage ratio of adjusted debt to capital was 0.5 at May 31, 2011. Under this financial covenant, our additional borrowing capacity is capped, although this covenant continues to provide us with ample liquidity, if needed. We are in compliance with this and all other restrictive covenants of our revolving credit agreement and do not expect the covenants to affect our operations, including our liquidity or borrowing capacity. As of May 31, 2011, no commercial paper was outstanding and the entire $1 billion under the revolving credit facility was available for future borrowings.

We issue other financial instruments in the normal course of business to support our operations, including letters of credit and surety bonds. We had a total of $619 million in letters of credit outstanding at May 31, 2011, with $93 million unused under our primary $500 million letter of credit facility, and $460 million in outstanding surety bonds placed by third-party insurance providers. These instruments are required under certain U.S. self-insurance programs and are also used in the normal course of international operations. The underlying liabilities insured by these instruments are reflected in our balance sheets, where applicable. Therefore, no additional liability is reflected for the letters of credit and surety bonds themselves.

Our capital lease obligations include leases for aircraft and facilities. Our facility leases include leases that guarantee the repayment of certain special facility revenue bonds that have been issued by municipalities primarily to finance the acquisition and construction of various airport facilities and equipment. These bonds require interest payments at least annually, with principal payments due at the end of the related lease agreement.