Property, Plant and Equipment

Oil and Natural Gas Properties. As of December 31, 2019 and 2018, we had approximately $3.4 billion and $3.8 billion, respectively, of total property, plant, and equipment, net of accumulated depreciation, depletion, and amortization on our balance sheet, substantially all of which relates to proved oil and natural gas properties.

Our capitalized costs related to proved oil and natural gas properties by area for the periods ended December 31 were as follows:



	2019			2018
	(in millions)
Proved
Eagle Ford	$	4,266		$	3,898
Northeastern Utah	1,331			1,659
Permian	1,791			1,787
Total Proved	7,388			7,344
Less accumulated depletion	(3,990		)	(3,607		)
Net capitalized costs for oil and natural gas properties	$	3,398		$	3,737

As of December 31, 2019, we did not have any suspended wells and as of December 31, 2018, suspended well costs were not material.

Asset Retirement Obligations. We have legal asset retirement obligations associated with the retirement of our oil and natural gas wells and related infrastructure. We settle these obligations when production on those wells is exhausted, when we no longer plan to use them or when we abandon them. We accrue these obligations when we can estimate the timing and amount of their settlement.

In estimating the liability associated with our asset retirement obligations, we utilize several assumptions, including a credit-adjusted risk-free rate between 7 percent and 9 percent on a majority of our obligations and a projected inflation rate of 2.5 percent. Changes in estimates in the table below represent changes to the expected amount and timing of payments to settle our asset retirement obligations. Typically, these changes primarily result from obtaining new information about the timing of our obligations to plug and abandon oil and natural gas wells and the costs to do so, or reassessing our assumptions in light of changing market conditions. The net asset retirement liability as of December 31 on our consolidated balance sheet in other current and non-current liabilities and the changes in the net liability for the periods ended December 31 were as follows:



	2019			2018
	(in millions)
Net asset retirement liability at January 1	$	42		$	35
Liabilities incurred	1			1
Liabilities settled	(1		)	—
Accretion expense	3			3
Changes in estimate	—			3
Net asset retirement liability at December 31	$	45		$	42

Capitalized Interest. Interest expense is reflected in our financial statements net of capitalized interest. We capitalize interest primarily on the costs associated with drilling and completing wells until production begins using a weighted average interest rate on our outstanding borrowings. Capitalized interest for both the years ended December 31, 2019 and 2018 was approximately $5 million. Subsequent to filing for Chapter 11 relief as further described in Note 1A, we only capitalize interest on those debt obligations for which interest will continue to be paid and which are not classified as liabilities subject to compromise.