However, he added that low oil prices may complicate matters for potential buyers of Zions and Comerica because they both have exposure to the energy sector given their geographic footprint. None of the potential buyers could be reached. Two recently announced transactions -- BB&T's $2.5 billion acquisition of Susquehanna Bancshares Inc. ( SUSQ ) and RBC's ( RY ) $5.4 billion City National Corp. ( CYN ) deal -- suggest the Fed may be more supportive of regional bank mergers in the months to come. "The general rule of thumb is that the buyer's regulatory rating is more important than seller's regulatory rating, so even underperforming banks can sell to the right acquirer," he said. "The Fed has finally given the green light to consolidation among regional banks."