JKX said well Z-05 in the Zaplavskoye license area in eastern Ukraine flowed at a rate of 4.6 million cubic feet per day.
"The encouraging well result supports our continuing appraisal of this part of the Zaplavskoye licence," JXK Chief Executive Officer Paul Davies said in a statement.
The company, which has headquarters in London, said second quarter production of 11,100 barrels of oil equivalent per day was split between Ukraine and Russia, with the latter accounting for the bulk of the gains. JXK said a "small contribution" came from operations in Hungary.
The Ukrainian government said there may be enough natural gas in shale reserve areas to meet the country's needs without imports.