KIEV, Sept. 29 - Naftogaz Ukrayiny on Thursday signed a preliminary agreement with ExxonMobil Corp for joint development of unconventional hydrocarbons in Ukraine.

This is the third paper signed between the two companies since February, underscoring the interest of the U.S. oil major in tapping resources in Ukraine.

A Naftogaz reported the signing of the agreement in a statement, but refused to give more details on the agreement.