Ukraine\'s state-run energy company Naftogaz has signed preliminary agreements on exploring domestic gas deposits with two U.S. companies, local media reported Friday. An agreement with ExxonMobil is related to shale gas and methane development in western Ukraine and the Donetsk-Dnieper Valley. Under a contract with Halliburton, the U.S. company will be responsible for monitoring, maintenance, construction and operation of oil and gas wells in Ukraine. The companies did not disclose any details of the two deals signed Thursday. Ukraine, which largely depends on Russian gas imports, wants to increase production and find alternative energy sources. Naftogaz and Royal Dutch Shell last month signed an 800-million-U.S. dollar deal on shale gas exploration and production. Ukraine\'s shale gas reserves are estimated at 1.5 trillion cubic meters.