eog utilized average prices per acre from comparable market transactions and estimated discounted cash flows as the basis for determining the fair value of unproved and proved properties , respectively , received in non-cash property exchanges .
see note 10 .
fair value of debt .
at december 31 , 2018 and 2017 , respectively , eog had outstanding $ 6040 million and $ 6390 million aggregate principal amount of senior notes , which had estimated fair values of approximately $ 6027 million and $ 6602 million , respectively .
the estimated fair value of debt was based upon quoted market prices and , where such prices were not available , other observable ( level 2 ) inputs regarding interest rates available to eog at year-end .
14 .
accounting for certain long-lived assets eog reviews its proved oil and gas properties for impairment purposes by comparing the expected undiscounted future cash flows at a depreciation , depletion and amortization group level to the unamortized capitalized cost of the asset .
the carrying values for assets determined to be impaired were adjusted to estimated fair value using the income approach described in the fair value measurement topic of the asc .
in certain instances , eog utilizes accepted offers from third-party purchasers as the basis for determining fair value .
during 2018 , proved oil and gas properties with a carrying amount of $ 139 million were written down to their fair value of $ 18 million , resulting in pretax impairment charges of $ 121 million .
during 2017 , proved oil and gas properties with a carrying amount of $ 370 million were written down to their fair value of $ 146 million , resulting in pretax impairment charges of $ 224 million .
impairments in 2018 , 2017 and 2016 included domestic legacy natural gas assets .
amortization and impairments of unproved oil and gas property costs , including amortization of capitalized interest , were $ 173 million , $ 211 million and $ 291 million during 2018 , 2017 and 2016 , respectively .
15 .
asset retirement obligations the following table presents the reconciliation of the beginning and ending aggregate carrying amounts of short-term and long-term legal obligations associated with the retirement of property , plant and equipment for the years ended december 31 , 2018 and 2017 ( in thousands ) : .

2018
2017
Carrying Amount at Beginning of Period
$946,848
$912,926
Liabilities Incurred
79,057
54,764
Liabilities Settled<sup>(1)</sup>
(70,829)
(61,871)
Accretion
36,622
34,708
Revisions
(38,932)
(9,818)
Foreign Currency Translations
1,611
16,139
Carrying Amount at End of Period
$954,377
$946,848
Current Portion
$26,214
$19,259
Noncurrent Portion
$928,163
$927,589

( 1 ) includes settlements related to asset sales .
the current and noncurrent portions of eog's asset retirement obligations are included in current liabilities - other and other liabilities , respectively , on the consolidated balance sheets. .

Question: Analyse this data from a financial earnings document. what is the percentage of the carrying amount of proved oil and gas properties concerning the total carrying amount in 2017?
Choices:
0.40529
-5.22385
0.39888
149.95739
375.94277
Correct choice index: 0