A worker walks past a pump jack on an oil field owned by Bashneft company near the village of Nikolo-Berezovka, northwest from Ufa, Bashkortostan, Russia, in this January 28, 2015 file photo. REUTERS/Sergei Karpukhin
A worker walks past a pump jack on an oil field owned by Bashneft company near the village of Nikolo-Berezovka, northwest from Ufa, Bashkortostan, Russia, in this January 28, 2015 file photo. REUTERS/Sergei Karpukhin