	September 30, 2020			December 31, 2019
Senior Notes	$	150,000		$	150,000
Credit Facility		116,000			157,000
Total debt		266,000			307,000
Less: Debt issuance costs		(1,434	)		(1,717	)
Less: Current maturities of long-term debt		(75,000	)		—
Long-term debt, net	$	189,566		$	305,283

We have two series of senior notes outstanding with an aggregate principal amount of $150 million ("Senior Notes") issued in a private placement transaction. Series A consists of $75 million in aggregate principal amount of notes that bear interest at a fixed rate of 4.01% and are due in full on September 30, 2021. Series B consists of $75 million in aggregate principal amount of notes that bear interest at a fixed rate of 4.11% and are due in full on September 30, 2023. Interest on each series of the Senior Notes is payable semi-annually on March 30 and September 30.

On June 22, 2020, we entered into Amendment No. 1 (the “Amendment”) to the Seventh Amended and Restated Credit Agreement, dated June 19, 2018 (as amended, the “Credit Facility”). The Amendment increases the maximum leverage ratio permitted under the Credit Facility for certain periods. Pursuant to the terms of the Amendment, the maximum leverage ratio permitted under the Credit Facility is as follows:

Quarter ending	Maximum leverage ratio permitted
June 30, 2020		3.00
September 30, 2020		3.00
December 31, 2020		3.00
March 31, 2021		3.00
June 30, 2021		3.00
September 30, 2021		2.75
December 31, 2021 and thereafter		2.50

Moreover, the Amendment modified the range of variable interest rates that the Credit Facility may bear to be a range from LIBOR plus 1.500% to LIBOR plus 2.875% and included the addition of a LIBOR floor of 0.50%. The Amendment also reduced the aggregate borrowing commitment under the Credit Facility to $225 million and the amount by which we may elect to increase the facility size, known as the “accordion” feature, to $50 million, subject to the satisfaction of certain conditions. Any outstanding balance under the Credit Facility is due on maturity on June 19, 2023. Our available capacity at any point in time is reduced by outstanding borrowings and outstanding letters of credit which totaled $13.3 million at September 30, 2020,

resulting in an available borrowing capacity under the Credit Facility of $95.7 million. In addition to indebtedness under the Credit Facility, we had $6.6 million of outstanding letters of credit and performance guarantees and bonds from other sources as at September 30, 2020.

The Credit Facility remains unsecured, and contains customary representations, warranties, terms and conditions for similar types of facilities.

The terms of the Credit Facility and Senior Notes require us to meet certain covenants, including, but not limited to, an interest coverage ratio (calculated as consolidated EBITDA divided by interest expense) and a leverage ratio (calculated as consolidated net indebtedness divided by consolidated EBITDA), where consolidated EBITDA (as defined in each agreement) and interest expense are calculated using the most recent four fiscal quarters. The Credit Facility and Senior Notes each include a cross-default provision, whereby a default under one agreement may trigger a default in the other agreement. The Credit Facility has more restrictive covenants with a minimum interest coverage ratio of 3.0 to 1.0 and permits a maximum leverage ratio as described above. The Credit Facility allows non-cash charges such as impairment of assets, stock compensation and other non-cash charges to be added back in the calculation of consolidated EBITDA. The terms of our Credit Facility also allow us to negotiate in good faith to amend any ratio or requirement to preserve the original intent of the agreement if any change in accounting principles would affect the computation of any financial ratio or covenant of the Credit Facility. In accordance with the terms of the Credit Facility, our leverage ratio is 2.49, and our interest coverage ratio is 5.39, each for the period ended September 30, 2020. We believe that we are in compliance with all covenants contained in our Credit Facility and Senior Notes. Our parent, Core Laboratories N.V., together with certain of our material, wholly-owned subsidiaries, are guarantors or co-borrowers under the Credit Facility and Senior Notes.

We entered into two interest rate swap agreements for a total notional amount of $50 million, including one of which was entered during the nine months ended September 30, 2020. See Note 16, Derivative Instruments and Hedging Activities for additional information.

The estimated fair value of total debt at September 30, 2020 and December 31, 2019 approximated the book value of total debt. The fair value was estimated using Level 2 inputs by calculating the sum of the discounted future interest and principal payments through the maturity date.

During the three months ended September 30, 2020, the Company incurred approximately $1.5 million in professional service fees and expenses associated with the evaluation of various corporate debt issuances and/or debt refinancing opportunities. These corporate finance and capital structure costs were expensed immediately and classified as interest expense.

Subsequent to the three months ended September 30, 2020, on October 16, 2020, we, along with Core Laboratories (U.S.) Interests Holdings, Inc. as issuer, entered into two new series of senior notes with aggregate principal amount of $60 million in a private placement transaction (“2020 Senior Notes”). The 2020 Senior Notes are scheduled to be issued and funded on January 12, 2021. Series A of the 2020 Senior Notes consists of $45 million in aggregate principal amount that bear interest at a fixed rate of 4.09% and are due in full on January 12, 2026. Series B of the 2020 Senior Notes consists of $15 million in aggregate principal amount that bear interest at a fixed rate of 4.38% and are due in full on January 12, 2028. Interest on each series of the 2020 Senior Notes is payable semi-annually on June 30 and December 30, commencing on June 30, 2021.

The terms of the 2020 Senior Notes require us to meet certain covenants, including, but not limited to, an interest coverage ratio (calculated as consolidated EBITDA divided by interest expense) and a leverage ratio (calculated as consolidated net indebtedness divided by consolidated EBITDA), where consolidated EBITDA (as defined in the Note Purchase Agreement) and interest expense are calculated using the most recent four fiscal quarters; and a priority indebtedness ratio (calculated as Priority Indebtedness divided by Consolidated Total Assets (as defined in the Notes Purchase Agreement.) The financial covenants for the 2020 Senior Notes Agreement are aligned with the Credit Facility and the associated Note Purchase Agreement also allows renegotiation of the ratios in consideration of changes in accounting principles. Our parent, Core Laboratories N.V., together with certain of our material, wholly-owned subsidiaries, are guarantors or co-borrowers under the 2020 Senior Notes.