Kiev - Ukraine and US energy giant Chevron signed a $10bn shale gas deal on Tuesday that the ex-Soviet nation hopes could end its energy dependence on Russia by 2020.
The production-sharing agreement allows Chevron to explore the Olesky deposit in western Ukraine that Kiev estimates can hold 2.98 trillion cubic meters of gas.
The deal comes close on the heels of similar agreements Ukraine struck in the past year with the Anglo-Dutch group Shell and the US super-major ExxonMobil.
"The implementation of large-scale projects with Shell and Chevron ... will enable Ukraine to fully meet its natural gas need by 2020," Ukrainian President Viktor Yanukovych said moments before Tuesday's signing ceremony.
Ukrainian Prime Minister Mykola Azarov has estimated the deal's value at $10bn (€7.4bn).
The Chevron agreement comes as part of a drive by Ukraine to diversify energy sources at a time when it is seeking to cement closer relations with the European Union at Russia's expense.
Russia last week slapped Ukraine with a gas bill of nearly $1bn in apparent anger at Kiev's bid to strike an EU free trade and political association agreement in Vilnius at the end of the month.
The EU deal's signature is seen as a first step in Ukraine's eventual membership in the 28-nation bloc.
But Moscow wants to see Ukraine join a Russian-led customs union that already includes Belarus and Kazakhstan.
Russia's energy giant Gazprom has denied presenting the massive gas bill to Ukraine as part of a strategy to force Kiev to reconsider the EU pact.
Ukraine has been moving swiftly to explore shale gas deposits which it lacks the technology to develop on its own but which it views as a key plank of a future energy strategy.
Ukraine and the Anglo-Dutch group Shell in January signed a $10bn production-sharing agreement to explore shale gas at the Yuzovska deposit in the eastern Donetsk region that may hold up to three trillion cubic metres of gas.
Ukraine in September also reached a production-sharing agreement with a consortium led by Exxon and Shell to extract natural gas on the Skifski site off Ukraine's Black Sea coast.
This site is expected to provide 8.0-10.0 billion cubic metres of natural gas per year.