; (B) reported in accordance with subsection (d); and (C) achieved within the same State as is served by the retail electricity supplier or retail natural gas supplier. (3) Exception Notwithstanding paragraph (2)(C), a State regulatory authority may authorize a retail electricity supplier or a retail natural gas supplier regulated by the State regulatory authority to purchase savings achieved in a different State, if— (A) the savings are achieved within the same power pool; and (B) the State regulatory authority that regulates the purchaser oversees the measurement and verification of the savings pursuant to the procedures and standards applicable in the State in which the purchaser is located. (4) Regulatory approval Nothing in this subsection limits or affects the authority of a State regulatory authority to require a retail electricity supplier or retail natural gas supplier that is regulated by the State regulatory authority to obtain the authorization or approval of the State regulatory authority of a contract for transfer of electricity savings or natural gas savings under this subsection. (5) Limitations To optimize the achievement of cost-effective efficiency potential, the Secretary may prescribe such limitations as the Secretary determines appropriate with respect to the proportion of the compliance obligation of a retail electricity or natural gas supplier under the applicable performance standards under subsection (d) that may be met using electricity savings or natural gas savings that are purchased under this subsection. (f) Measurement and verification of savings The regulations promulgated pursuant to subsection (c) shall include— (1) procedures and standards for defining and measuring electricity savings and natural gas savings that can be counted towards the performance standards established under subsection (d), that shall— (A) specify the types of energy efficiency and energy conservation measures that can be counted