Prosperity Bancshares to Merge with American State Financial Corporation

Prosperity Bancshares, Inc.®

, the parent company of Prosperity Bank®, announced today the signing of a definitive merger agreement with American State Financial Corporation and its wholly owned subsidiary American State Bank whereby American State Bank will be merged with and into Prosperity Bank. This is the fourth transaction announced by Prosperity within the past few months. American State Bank operates thirty-seven (37) banking offices in eighteen (18) counties across West Texas. As of December 31, 2011, ASB, on a consolidated basis, reported total assets of $3.08 billion, total loans of $1.21 billion and total deposits of $2.46 billion. Under the terms of the definitive agreement, Prosperity will issue up to 8,525,000 shares of Prosperity common stock plus $178.5 million in cash for all outstanding shares of American State Financial Corporation capital stock, subject to certain conditions and potential adjustment.