considering the years 2016 and 2017 , what is the average current portion?
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 rr 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 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 . during 2016 , proved oil and gas properties with a carrying rr amount of $ 643 million were written down to their fair value of $ 527 million , resulting in pretax impairment charges of $ 116 million . impairments in 2017 , 2016 and 2015 included domestic legacy natural gas assets . amortization and impairments of unproved oil and gas property costs , including amortization of capitalized interest , were $ 211 million , $ 291 million and $ 288 million during 2017 , 2016 and 2015 , 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 , 2017 and 2016 ( in thousands ) : .

|  | 2017 | 2016 |
| :--- | :--- | :--- |
| Carrying Amount at Beginning of Period | $912,926 | $811,554 |
| Liabilities Incurred<sup>(1)</sup> | 54,764 | 212,739 |
| Liabilities Settled<sup>(2)</sup> | (61,871) | (94,800) |
| Accretion | 34,708 | 32,306 |
| Revisions | (9,818) | (38,286) |
| Foreign Currency Translations | 16,139 | (10,587) |
| Carrying Amount at End of Period | $946,848 | $912,926 |
| Current Portion | $19,259 | $18,516 |
| Noncurrent Portion | $927,589 | $894,410 |

( 1 ) includes $ 164 million in 2016 related to yates transaction ( see note 17 ) . ( 2 ) 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. .

table_row = [19259, 18516] # row labeled current portion
a = sum(table_row) / len(table_row)