LONG-TERM DEBT

Our long-term debt consisted of the following (dollars in thousands):



	Interest rate at March 31, 2018	March 31, 2018		December 31, 2017
Senior unsecured notes due 2022	5.625%	400,000		400,000
Senior unsecured notes due 2023	5.625%	350,000		350,000
Senior unsecured notes due 2025	6.375%	325,000		325,000
Senior unsecured notes due 2026	7.250%	300,000		300,000
SemGroup $1.0 billion corporate revolving credit facility⁽¹⁾
Eurodollar borrowings		—		131,000
HFOTCO acquisition final payment	8.000%	578,441		565,868
HFOTCO term loan B ⁽²⁾	5.800%	530,750		532,125
HFOTCO tax exempt notes payable due 2050	2.816%	225,000		225,000
HFOTCO $75 million revolving credit facility⁽³⁾	5.403%	60,000		60,000
Capital leases		27		25
Unamortized premium (discount) and debt issuance costs, net		(29,734	)	(30,398	)
Total long-term debt, net		2,739,484		2,858,620



Less: current portion of long-term debt	5,527		5,525
Noncurrent portion of long-term debt, net	$	2,733,957	$	2,853,095


(1)	SemGroup $1.0 billion corporate revolving credit facility matures on March 15, 2021.


(2)	HFOTCO term loan B is due in quarterly installments of $1.4 million with a final payment due on August 19, 2021.


(3)	HFOTCO $75 million revolving credit facility matures on August 19, 2019.

HFOTCO acquisition final payment

On April 17, 2018, we made the final payment related to the HFOTCO acquisition in the amount of $579.6 million. The payment was funded through revolving credit facility borrowings and cash on hand.

Pledges and guarantees

Our senior unsecured notes are guaranteed by certain subsidiaries. See Note 15 for additional information.

Our $1.0 billion corporate revolving credit facility is guaranteed by all of SemGroup’s material wholly-owned domestic subsidiaries, with the exception of Maurepas Pipeline LLC and HFOTCO, and secured by a lien on substantially all of the property and assets of SemGroup Corporation and the other loan parties, subject to customary exceptions.

The HFOTCO term loan B, HFOTCO tax exempt notes payable and HFOTCO $75 million revolving credit facility are secured by substantially all of the assets of HFOTCO and its immediate parent, Buffalo Gulf Coast Terminals LLC. The HFOTCO tax exempt notes payable have a priority position over the HFOTCO term loan B and HFOTCO revolving credit facility.

Letters of credit

We had the following outstanding letters of credit at March 31, 2018 (dollars in thousands):



SemGroup $1.0 billion revolving credit facility	2.25%	$	39,385
Secured bi-lateral⁽¹⁾	1.75%	$	55,409

(1) Secured bi-lateral letters of credit are external to the SemGroup $1.0 billion revolving credit facility and do not reduce availability for borrowing on the credit facility.

Capitalized interest

During the three months ended March 31, 2018 and 2017, we capitalized interest of $3.1 million and $5.6 million, respectively.

Fair value

We estimate the fair value of our senior unsecured notes based on unadjusted, transacted market prices near the measurement date. Our other long-term debts are estimated to be carried at fair value as a result of the recent timing of borrowings or rate resets. We estimate the fair value of our consolidated long-term debt, including current maturities, to be approximately $2.7 billion at March 31, 2018, which is categorized as a Level 3 measurement due to certain unobservable inputs used to estimate the fair value of the final payment.