the principal components of eog's rollforward of valuation allowances for deferred income tax assets were as follows ( in thousands ) : .
considering the eog's roll forward of valuation allowances for deferred income tax assets during 2015-2017 , what was the lowest value registered in the beginning balance?
( 1 ) increase in valuation allowance related to the generation of tax nols and other deferred tax assets . ( 2 ) decrease in valuation allowance associated with adjustments to certain deferred tax assets and their related allowance . ( 3 ) represents dispositions/revisions/foreign exchange rate variances and the effect of statutory income tax rate changes . as of december 31 , 2017 , eog had state income tax nols being carried forward of approximately $ 1.7 billion , which , if unused , expire between 2018 and 2036 . during 2017 , eog's united kingdom subsidiary incurred a tax nol of approximately $ 72 million which , along with prior years' nols of $ 857 million , will be carried forward indefinitely . eog also has united states federal and canadian nols of $ 335 million and $ 158 million , respectively , with varying carryforward periods . eog's remaining amt credits total $ 798 million , resulting from amt paid with respect to prior years and an increase of $ 41 million in 2017 . as described above , these nols and credits , as well as other less significant future income tax benefits , have been evaluated for the likelihood of utilization , and valuation allowances have been established for the portion of these deferred income tax assets that t do not meet the "more likely than not" threshold . as further described above , significant changes were made by the tcja to the corporate amt that are favorable to eog , including the refunding of amt credit carryovers . due to these legislative changes , eog intends to settle certain uncertain tax positions related to amt credits for taxable years 2011 through 2015 , resulting in a decrease of uncertain tax positions of $ 40 million . the amount of unrecognized tax benefits at december 31 , 2017 , was $ 39 million , resulting from the tax treatment of its research and experimental expenditures related to certain innovations in its horizontal drilling and completion projects , which ish not expected to have an earnings impact . eog records interest and penalties related to unrecognized tax benefits to its income tax provision . eog does not anticipate that the amount of the unrecognized tax benefits will increase during the next twelve months . eog and its subsidiaries file income tax returns and are subject to tax audits in the united states and various state , local and foreign jurisdictions . eog's earliest open tax years in its principal jurisdictions are as follows : united states federal ( 2011 ) , canada ( 2014 ) , united kingdom ( 2016 ) , trinidad ( 2011 ) and china ( 2008 ) . eog's foreign subsidiaries' undistributed earnings are no longer considered to be permanently reinvested outside the u.s . and , accordingly , eog has cumulatively recorded $ 20 million of foreign and state deferred income taxes as of december 31 , 2017 . 7 . employee benefit plans stock-based compensation during 2017 , eog maintained various stock-based compensation plans as discussed below . eog recognizes compensation expense on grants of stock options , sars , restricted stock and restricted stock units , performance units and grants made under the eog resources , inc . employee stock purchase plan ( espp ) . stock-based compensation expense is calculated based upon the grant date estimated fair value of the awards , net of forfeitures , based upon eog's historical employee turnover rate . compensation expense is amortized over the shorter of the vesting period or the period from date of grant until the date the employee becomes eligible to retire without company approval. .