eog resources , inc . supplemental information to consolidated financial statements ( continued ) net proved undeveloped reserves . the following table presents the changes in eog's total proved undeveloped reserves during 2018 , 2017 and 2016 ( in mboe ) : .
considering the changes in eog's total proved undeveloped reserves during 2018 , 2017 , and 2016 , what is the average value of extensions and discoveries?
for the twelve-month period ended december 31 , 2018 , total puds increased by 217 mmboe to 1380 mmboe . eog added approximately 31 mmboe of puds through drilling activities where the wells were drilled but significant expenditures remained for completion . based on the technology employed by eog to identify and record puds ( see discussion of technology employed on pages f-36 and f-37 of this annual report on form 10-k ) , eog added 460 mmboe . the pud additions were primarily in the permian basin , anadarko basin , the eagle ford and , to a lesser extent , the rocky mountain area , and 80% ( 80 % ) of the additions were crude oil and condensate and ngls . during 2018 , eog drilled and transferred 266 mmboe of puds to proved developed reserves at a total capital cost of $ 2745 million . all puds , including drilled but uncompleted wells ( ducs ) , are scheduled for completion within five years of the original reserve booking . for the twelve-month period ended december 31 , 2017 , total puds increased by 110 mmboe to 1163 mmboe . eog added approximately 38 mmboe of puds through drilling activities where the wells were drilled but significant expenditures remained for completion . based on the technology employed by eog to identify and record puds , eog added 199 mmboe . the pud additions were primarily in the permian basin and , to a lesser extent , the eagle ford and the rocky mountain area , and 74% ( 74 % ) of the additions were crude oil and condensate and ngls . during 2017 , eog drilled and transferred 153 mmboe of puds to proved developed reserves at a total capital cost of $ 1440 million . revisions of puds totaled positive 33 mmboe , primarily due to updated type curves resulting from improved performance of offsetting wells in the permian basin , the impact of increases in the average crude oil and natural gas prices used in the december 31 , 2017 , reserves estimation as compared to the prices used in the prior year estimate , and lower costs . during 2017 , eog sold or exchanged 8 mmboe of puds primarily in the permian basin . for the twelve-month period ended december 31 , 2016 , total puds increased by 7 mmboe to 1053 mmboe . eog added approximately 21 mmboe of puds through drilling activities where the wells were drilled but significant expenditures remained for completion . based on the technology employed by eog to identify and record puds , eog added 117 mmboe . the pud additions were primarily in the permian basin and , to a lesser extent , the rocky mountain area , and 82% ( 82 % ) of the additions were crude oil and condensate and ngls . during 2016 , eog drilled and transferred 149 mmboe of puds to proved developed reserves at a total capital cost of $ 1230 million . revisions of puds totaled positive 64 mmboe , primarily due to improved well performance , primarily in the delaware basin , and lower production costs , partially offset by the impact of decreases in the average crude oil and natural gas prices used in the december 31 , 2016 , reserves estimation as compared to the prices used in the prior year estimate . during 2016 , eog sold 46 mmboe of puds primarily in the haynesville play. .