Under the TCA, the parties to the agreement delegated to AEPSC the responsibility of monitoring the reliability of their transmission systems and administering the OATT on their behalf. The allocations have been governed by the FERC-approved OATT for the SPP. Additional costs for transmission services provided by AEPTCo and other transmission affiliates are billed to PSO and SWEPCo through the SPP OATT. PSO, SWEPCo and AEPSC are parties to the TCA in connection with the operation of the transmission assets of PSO and SWEPCo. The TCA has been approved by the FERC and establishes a coordinating committee, which is charged with overseeing the coordinated planning of the transmission facilities of the parties to the agreement. This includes the performance of transmission planning studies, the interaction of such companies with independent system operators and other regional bodies interested in transmission planning and compliance with the terms of the OATT filed with the FERC and the rules of the FERC relating to such a tariff. The following table shows the net transmission service charges recorded by PSO and SWEPCo: The charges shown above are recorded in Other Operation expenses on the statements of income. AEPTCo provides transmission services to affiliates in accordance with the OATT, TA and TCA. AEPTCo recorded affiliated transmission revenues in Sales to AEP Affiliates on the statements of income. Refer to the Affiliated Revenues and Purchases section above for amounts related to these transactions. Pursuant to an order from the PUCT, ETT bills AEP Texas for its ERCOT wholesale transmission services. ETT billed AEP Texas $28 million, $27 million and $27 million for transmission services in 2020, 2019 and 2018, respectively. The billings are recorded in Other Operation expenses on AEP Texas’ statements of income. In 2007, AEP Texas entered into a PPA with an affiliate, AEPEP, whereby AEP Texas agreed to sell AEPEP 100% of AEP Texas’ capacity and associated energy from its undivided interest (54.69%) in the Oklaunion Power Station. The PPA was approved by the FERC. In September 2018, the co-owners of Oklaunion Power Station voted to close the plant in 2020. Effective October 2018, AEP Texas increased depreciation expense to ensure the plant balances are fully depreciated as of September 2020 and recovered through the PPA billings to AEPEP. Under the early termination provisions of the PPA, AEPEP paid AEP Texas the full Property, Plant and Equipment balance through depreciation payments until termination of the PPA due to the plant closing in September 2020. See “Dispositions” section of Note 7 for additional information. AEP Texas recorded revenue of $88 million, $157 million and $104 million from AEPEP for the years ended December 31, 2020, 2019 and 2018, respectively. These amounts are included in Sales to AEP Affiliates on AEP Texas’ statements of income. 385 Oklaunion PPA between AEP Texas and AEPEP (Applies to AEP Texas) ERCOT Transmission Service Charges (Applies to AEP and AEP Texas) Years Ended December 31, Company 2020 2019 2018 (in millions) PSO $ 69.7  $ 46.9  $ 65.9  SWEPCo 31.3  20.1  10.5 