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REGULATORY ASSETS AND LIABILITIES (Notes)
 12 Months Ended
Dec. 31, 2024
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items]  
Schedule of Regulatory Assets and Liabilities REGULATORY ASSETS AND LIABILITIES
The tables below present a summary of regulatory assets and liabilities, net of amortization, for the periods indicated:

December 31, 2024
Recovery PeriodCurrentNoncurrentTotal
(Thousands of dollars)
Winter weather event costs(a)$9,051 $15,938 $24,989 
Under-recovered purchased-gas costs1 year43,819 — 43,819 
Pension and postemployment benefit costs, net
See Note 11
1,358 224,837 226,195 
Reacquired debt costs4 years723 1,989 2,712 
MGP remediation costs15 years1,000 30,067 31,067 
Ad-valorem tax1 year14,066 — 14,066 
WNA1 year26,684 — 26,684 
Customer credit deferrals1 year255 3,639 3,894 
Other, net1 to 20 years4,254 1,536 5,790 
Total regulatory assets101,210 278,006 379,216 
Income tax rate changes(a)— (467,563)(467,563)
Over-recovered purchased-gas costs1 year(22,525)— (22,525)
Total regulatory liabilities(22,525)(467,563)(490,088)
Net regulatory assets and liabilities$78,685 $(189,557)$(110,872)
(a) Recovery period varies by jurisdiction. See discussion below for additional information regarding our regulatory assets related to winter weather event costs and regulatory liabilities related to income tax rate changes.

December 31, 2023
Recovery PeriodCurrentNoncurrentTotal
(Thousands of dollars)
Winter weather event costs(a)$22,633 $21,495 $44,128 
Under-recovered purchased-gas costs1 year10,391 — 10,391 
Pension and postemployment benefit costs
See Note 11
6,379 228,092 234,471 
Reacquired debt costs6 years723 2,712 3,435 
MGP remediation costs15 years98 31,893 31,991 
Ad-valorem tax1 year14,533 — 14,533 
WNA1 year11,404 — 11,404 
Customer credit deferrals1 year6,184 — 6,184 
Other1 to 18 years2,963 3,714 6,677 
Total regulatory assets75,308 287,906 363,214 
Income tax rate changes(a)— (500,478)(500,478)
Over-recovered purchased-gas costs1 year(66,901)— (66,901)
Total regulatory liabilities(66,901)(500,478)(567,379)
Net regulatory assets and liabilities$8,407 $(212,572)$(204,165)
(a) Recovery period varies by jurisdiction. See discussion below for additional information regarding our regulatory assets related to winter weather event costs and regulatory liabilities related to income tax rate changes.

Regulatory assets in our consolidated balance sheets, as authorized by various regulatory authorities, are probable of recovery. Base rates and certain riders are designed to provide a recovery of costs during the period such rates are in effect, but do not generally provide for a return on investment for amounts we have deferred as regulatory assets. All of our regulatory assets are subject to review by the respective regulatory authorities during future regulatory proceedings.
Other regulatory assets and liabilities - Purchased-gas costs represent the natural gas costs that have been over- or under-recovered from customers through the purchased-gas cost adjustment mechanisms, and includes natural gas utilized in our operations and premiums paid and any cash settlements received from our purchased natural gas call options.

The OCC, KCC and regulatory authorities in Texas have approved the recovery of pension costs and other postemployment benefits costs through rates for Oklahoma Natural Gas, Kansas Gas Service and Texas Gas Service, respectively. The costs recovered through rates are based on the net periodic benefit cost for defined benefit pension and other postemployment costs.
Differences, if any, between the net periodic benefit cost (credit), net of deferrals, and the amount recovered through rates are reflected in earnings. We historically have recovered defined benefit pension and other postemployment benefit costs through rates. We believe it is probable that regulators will continue to include the net periodic pension and other postemployment benefit costs in our cost of service.

We amortize reacquired debt costs in accordance with the accounting guidelines prescribed by the OCC and the KCC.

See Note 15 for additional information regarding our regulatory assets for MGP remediation costs.

Ad-valorem tax represents the difference in Kansas Gas Service’s taxes incurred each year above or below the amount approved in base rates. This difference is deferred as a regulatory asset or liability for a 12-month period. Kansas Gas Service then applies an adjustment to customers’ bills to refund the over-collected revenue or bill the under-collected revenue over the subsequent 12 months.

Weather normalization represents revenue over- or under-recovered through the WNA rider in Kansas. This amount is deferred as a regulatory asset or liability for a 12-month period. Kansas Gas Service then applies an adjustment to customers’ bills for 12 months to refund the over-collected revenue or bill the under-collected revenue.

The customer credit deferrals and the noncurrent regulatory liability for income tax rate changes represents deferral of the effects of enacted federal and state income tax rate changes on our ADIT and the effects of these changes on our rates. See Note 12 for additional information regarding the impact of income tax rate changes.
Recovery through rates resulted in amortization of regulatory assets, net, of approximately $14.4 million, $14.7 million and $9.4 million for the years ended December 31, 2024, 2023 and 2022, respectively.