NEW YORK, Feb 11 (Reuters) - Brazil's state-owned oil firm Petrobras (PETR4.SA: Quote, Profile, Research)(PBR.N: Quote, Profile, Research) postponed on Monday the reopening of its global bond maturing 2018 due to "volatile market conditions," a market source said.

Petrobras was hoping to sell on Monday an additional $500 million of the bond, which carries a coupon of 6.125 percent.

It had originally sold $1 billion of the paper in November, and first reopened it last month, with an additional issue worth $750 million. (Reporting by Walter Brandimarte; Editing by Diane Craft)