Expansion-minded bank owner Park Sterling Corp. said Monday it is buying out an older North Carolina rival in a deal that would roughly double its size.

The owner of Charlotte-based Park Sterling Bank is paying about $77.8 million in cash and stock for Citizens South Bank, which has $1.1 billion in assets and 21 branches.

The sale is expected to close in the fourth quarter. The combined bank would have about $2.2 billion in total assets and 45 retail offices in the Carolinas and Georgia.

Park Sterling was founded in 2006. It more than doubled its size through its 2011 purchase of Greenwood-based Community Capital Corp., the holding company for the Upstate’s CapitalBank of South Carolina. Park Sterling opened its only Charleston office on East Bay Street about a year ago.

Citizens South was founded in 1904 and is based in Gastonia. Its website shows one South Carolina office, in Rock Hill.

“We believe this transformational partnership will be positive for our shareholders, customers, employees and communities. Citizens South’s footprint is virtually a perfect fit with Park Sterling’s,” said Park Sterling CEO Jim Cherry.

In discussing his bank’s quarterly earnings last week, Cherry said the company was on the lookout for deals.

“On the mergers and acquisitions front, we expect continued consolidation among community banks across the Carolinas and Virginia, driven in part by increased regulatory burden, uncertain economic conditions, distressed housing markets and challenging capital markets,” he said May 1. “We remain active in seeking attractive partners who share our vision of creating a profitable, growing regional franchise, characterized by sound risk management, superior customer service, and exceptional customer relationships.”