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 thereunder 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, 2022 and September 30, 2022, letters of credit totaled $4.4 million and $4.4 million, respectively, under our Revolving Credit Facility. As of December 31, 2022 and September 30, 2022, we had $1,145.6 million and $1,145.6 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, 2022, the estimated fair value of the 2027 Senior Notes was approximately $959.9 million. The fair value of the 2027 Senior Notes as of December 31, 2022 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 unpaid interest to the redemption date. On or after 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 accrued and unpaid interest on the redemption date.
The indenture pursuant to which the 2027 Senior Notes were issued contains customary events of default, including, among other things, payment default, exchange default, failure to provide notices thereunder and provisions related to bankruptcy events. The indenture also contains customary negative covenants.
We were in compliance with the covenants relating to the 2027 Senior Notes as of December 31, 2022.
Other Debt and Other Items
Other debt consists primarily of obligations under capital leases and loans, and unsecured credit facilities. The unsecured credit facilities are primarily used for standby letters of credit issued in connection with general and professional liability insurance programs and for contract performance guarantees. At December 31, 2022 and September 30, 2022, these outstanding standby letters of credit totaled $871.1 million and $640.3 million, respectively. As of December 31, 2022, we had $425.0 million available under these unsecured credit facilities.
Effective Interest Rate
Our average effective interest rate on our total debt, including the effects of the interest rate swap and interest rate cap agreements, during the three months ended December 31, 2022 and 2021 was 5.1% and 3.4%, respectively.