Revolving Credit Facility will be adjusted on an annual basis based on our achievement of preset thresholds for each Sustainability Metric.
Some of our material subsidiaries (the "Guarantors") have guaranteed the obligations of the borrowers under the Credit Agreement, subject to certain exceptions. The borrowers' obligations under the Credit Agreement are secured by a lien on substantially all of our assets and our Guarantors' assets, subject to certain exceptions.
The Credit Agreement contains customary negative covenants that include, among other things, limitations on our ability and certain of our subsidiaries, subject to certain exceptions, to incur liens and debt, make investments, dispositions, and restricted payments, change the nature of their business, consummate mergers, consolidations and the sale of all or substantially all of their respective assets, taken as a whole, and transact with affiliates. We are also required to maintain a consolidated interest coverage ratio of at least 3.00 to 1.00 and a consolidated leverage ratio of less than or equal to 4.00 to 1.00 (subject to certain adjustments in connection with permitted acquisitions), tested on a quarterly basis (the "Financial Covenants"). Our consolidated leverage ratio was 2.40 to 1.00 at December 31, 2021. As of December 31, 2021, we were in compliance with the covenants of the Credit Agreement.
The Credit Agreement contains customary affirmative covenants, including, among other things, compliance with applicable law, preservation of existence, maintenance of properties and of insurance, and keeping proper books and records. The Credit Agreement contains customary events of default, including, among other things, nonpayment of principal, interest or fees, cross-defaults to other debt, inaccuracies of representations and warranties, failure to perform covenants, events of bankruptcy and insolvency, change of control and unsatisfied judgments, subject in certain cases to notice and cure periods and other exceptions.
On April 13, 2021, we entered into Amendment No. 10 to the Credit Agreement, pursuant to which the lenders thereunder provided a secured term “B” credit facility (the “Term B Facility”) to the Company in an aggregate principal amount of $700,000,000. The Term B Facility matures on April 13, 2028. The proceeds of the Term B Facility were used to fund the purchase price, fees and expenses in connection with our cash tender offer to purchase up to $700,000,000 aggregate purchase price (not including any accrued and unpaid interest) of our outstanding 5.875% Senior Notes due 2024.
The Term B Facility is subject to the same affirmative and negative covenants and events of default as the Term A Facility previously incurred pursuant to the existing Credit Agreement (except that the Financial Covenants in the Credit Agreement do not apply to the Term B Facility). The applicable interest rate for the Term B Facility is calculated at a per annum rate equal to, at our option, (a) the Eurocurrency Rate (as defined in the Credit Agreement) plus 1.75% or (b) the Base Rate (as defined in the Credit Agreement) plus 0.75%.
On June 25, 2021, we entered into Amendment No. 11 to the Credit Agreement, pursuant to which lenders have provided us with an additional $215,000,000 in aggregate principal amount under the Term A Facility. We used the net proceeds from the increase in the Term A Facility (together with cash on hand), to (i) redeem all of our remaining 5.875% Senior Notes due 2024 and (ii) pay fees and expenses related to such redemption.
At December 31, 2021 and September 30, 2021, letters of credit totaled $5.2 million and $5.2 million, respectively, under our Revolving Credit Facility. As of December 31, 2021 and September 30, 2021, we had $1,144.8 million and $1,144.8 million, respectively, available under our Revolving Credit Facility.
2027 Senior Notes
On February 21, 2017, we completed a private placement offering of $1,000,000,000 aggregate principal amount of our unsecured 5.125% Senior Notes due 2027 (the “2027 Senior Notes”). On June 30, 2017, we completed an exchange offer to exchange the unregistered 2027 Senior Notes for registered notes, as well as related guarantees.
As of December 31, 2021, the estimated fair value of the 2027 Senior Notes was approximately $1,052.1 million. The fair value of the 2027 Senior Notes as of December 31, 2021 was derived by taking the mid-point of the trading prices from an observable market input (Level 2) in the secondary bond market and multiplying it by the outstanding balance of the 2027 Senior Notes. Interest is payable on the 2027 Senior Notes at a rate of 5.125% per annum. Interest on the 2027 Senior Notes is payable semi-annually on March 15 and September 15 of each year, commencing on September 15, 2017. The 2027 Senior Notes will mature on March 15, 2027.
At any time and from time to time prior to December 15, 2026, we may redeem all or part of the 2027 Senior Notes, at a redemption price equal to 100% of their principal amount, plus a “make whole” premium as of the redemption date, and accrued and