Significant regulatory assets and liabilities as of March 31, 2018 and September 30, 2017 included the following:



	March 31, 2018		September 30, 2017
	(In thousands)
Regulatory assets:
Pension and postretirement benefit costs⁽¹⁾	$	20,918	$	26,826
Infrastructure mechanisms⁽²⁾	65,286		46,437
Deferred gas costs	—		65,714
Recoverable loss on reacquired debt	9,954		11,208
Deferred pipeline record collection costs	14,646		11,692
APT annual adjustment mechanism	—		2,160
Rate case costs	3,016		2,629
Other	8,064		10,132
	$	121,884	$	176,798
Regulatory liabilities:
Regulatory excess deferred taxes⁽³⁾	$	737,798	$	—
Regulatory cost of service reserve⁽⁴⁾	29,042		—
Regulatory cost of removal obligation	526,483		521,330
Deferred gas costs	167,036		15,559
Asset retirement obligation	12,827		12,827
APT annual adjustment mechanism	5,081		—
Other	14,740		5,941
	$	1,493,007	$	555,657


(1)	Includes $7.8 million and $9.4 million of pension and postretirement expense deferred pursuant to regulatory authorization.


(2)	Infrastructure mechanisms in Texas and Louisiana allow for the deferral of all eligible expenses associated with capital expenditures incurred pursuant to these rules, including the recording of interest on deferred expenses until the next rate proceeding (rate case or annual rate filing), at which time investment and costs would be recoverable through base rates.


(3)	The TCJA resulted in the remeasurement of the net deferred tax liability included in our rate base. The excess deferred taxes will be returned to utility customers in accordance with regulatory requirements. See Note 6 for further information.

(4)

Effective January 1, 2018, regulators in each of our service areas required us to establish a regulatory liability for the difference in recoverable federal taxes included in revenues based on the former 35% federal statutory rate and the new 21% federal statutory rate for service provided on or after January 1, 2018. This liability will be returned to utility customers in accordance with regulatory requirements. See Note 6 for further information.