A group representing holders of Oi SA's bonds not guaranteed by unit Telemar Norte Leste SA is growing, underscoring the challenges facing Brazil's largest fixed-line phone carrier as it enters bankruptcy protection proceedings, Reuters reported yesterday. New York-based investment bank Houlihan Lokey Inc and Metrica Investments LLC have stepped up talks with owners of $6.4 billion worth of euro- and U.S. dollar-denominated Oi bonds in the wake of the largest bankruptcy protection filing in Brazilian history. The Houlihan-Metrica group is one of the few gearing up for tough bankruptcy talks with Oi, which succumbed to a heavy debt burden and mounting competition after years of shareholder disputes. At 65.4 billion reais ($19.4 billion), Oi's petition is fraught with challenges due to a complex capital structure and wide creditor base, analysts said.