 Exhibit 99.1 Merger with American State Financial Corp February 27, 2012 |
 2 “Safe Harbor” Statement “Safe Harbor” Statement under the Private Securities Litigation Reform Act of 1995 Statements contained in this presentation which are not historical facts and which pertain to future operating results of Prosperity Bancshares ® and its subsidiaries constitute “forward-looking statements” within the meaning of the Private Securities Litigation reform Act of 1995. These forward-looking statements involve significant risks and uncertainties. Actual results may differ materially from the results discussed in these forward-looking statements. Factors that might cause such a difference include, but are not limited to, those discussed in the company’s periodic filings with the SEC. Copies of the SEC filings for Prosperity Bancshares ® may be downloaded from the Internet at no charge from www.prosperitybanktx.com. |
 3 Strategic Rationale Strategic Rationale • American State merger marks Prosperity’s entry into West Texas in a significant way: – Expands Prosperity west of I-35 and creates a presence in 18 new counties, for a total of 78 counties of operation upon completion – American State is ranked in the top three by deposit market share in each of the following attractive markets: Lubbock, Abilene and Odessa – Creates ample opportunities for in-market consolidation in new markets across Texas • Creates the second largest bank focused solely on Texas with approximately $14 billion in assets: – Improves Texas deposit market share ranking to the seventh position from number nine – Significantly increases the C&I loan portfolio, increasing from approximately $440 million to over $740 million – Complementary balance sheets as American State brings high quality, low cost deposits and pristine asset quality • Following the merger, Prosperity will be the 51st largest U.S. headquartered banking institution |
 4 Assumptions & Impact Assumptions & Impact • Expected to be approximately 8% accretive to earnings per share • The tangible common equity ratio is restored in approximately one year • Preliminary loan mark is approximately equal to American State’s current loan loss reserve • Non-deposit fee revenue is enhanced through the merger • Through the merger Prosperity will acquire a trust department with $850 million in assets under management |
 5 Pro Forma Branch Franchise Pro Forma Branch Franchise (1) PB pro forma for pending and recently completed acquisitions: Texas Bankers, East Texas Financial Services and Bank Arlington (2) ASFC excludes one drive thru branch in Odessa and eight mobile deposit services for nursing homes that do not retain deposits PB (1) (178) ASFC (2) (37) Texas Deposit Market Share Source: SNL Financial and Microsoft MapPoint; Deposit data as of June 30, 2011 |
 6 Merger Summary Merger Summary Merger Partner: American State Financial Corporation (“American State” or “ASFC”) Aggregate Value: $529.2 million (1) Termination Fee: $20.0 million (3.8% of transaction value) Due Diligence: Completed (1) Based on PB closing price of $41.14 on 2/24/2012 Consideration: 66.3% stock / 33.7% cash Each share of American State common stock will be converted into the right to receive the pro-rata share of $178.5 million in cash and 8,525,000 shares of PB common stock |
 7 Transaction Highlights Transaction Highlights (1) Based on PB closing price of $41.14 on 2/24/2012 (2) ASFC balance sheet and income statement data as of 12/31/2012; earnings estimates per PB management (3) Calculated as the premium paid to tangible book value as a percentage of total deposits Source: SNL Financial Anticipated Closing: Third Quarter 2012 Pre-tax Cost Savings: 20.0% Transaction Multiples: Merger Price to: (1),(2) Book Value: 1.89x Tang. Book Value: 2.06x LTM Earnings: 12.6x 2012 Earnings Estimate: 13.6x Deposit Premium: (3) 11.1% |
 8 Management Retention Management Retention The following members of American State’s management will join Prosperity’s executive team: Management Current Role Prosperity Position W. R. Collier Chairman & CEO - Holding Company Board Member - Senior Chairman – West Texas Area Michael F. Epps Vice Chairman & President - Chairman – West Texas Area - Prosperity Management Committee Tony Whitehead President – Lubbock Division - President – West Texas Area - Prosperity Management Committee Additionally, four Prosperity Bank board seats will be offered to the following American State Bank Directors: Directors Industry Scott Collier Construction Mark Kirkpatrick Ranching / Oil & Gas Van May Agribusiness Don Pickering Manufacturing |
 9 American State Financial Highlights American State Financial Highlights • Founded in 1948 in Lubbock, TX • Consistent growth and profitability through recession • Operates 37 locations across 18 counties • Established presence in core markets of operation Source: SNL Financial ($mm) At or for the year ended December 31, '08 - '11 2008 2009 2010 2011 CAGR Balance Sheet Total Assets $2,203.4 $2,406.7 $2,690.8 $3,081.7 11.8% Total Net Loans 979.7 1,036.5 1,073.7 1,174.3 6.2% Securities 1,000.9 1,149.5 1,225.1 1,587.8 16.6% Deposits 1,766.1 1,931.8 2,157.1 2,459.5 11.7% Total Equity 229.5 231.8 250.9 279.7 6.8% Balance Sheet Ratios Loans / Deposits (%) 56.5 54.9 51.0 49.3 TCE / TA (%) 9.45 8.75 8.53 8.38 Leverage Ratio (%) 9.49 8.79 8.82 8.15 Tier 1 Ratio (%) 15.71 15.30 16.37 15.03 Total Capital Ratio (%) 16.79 16.45 17.62 16.29 Profitability Ratios ROAA (%) 1.28 1.27 1.44 1.48 ROAE (%) 11.54 12.75 14.70 15.85 Net Interest Margin (%) 3.58 3.89 3.85 3.62 Efficiency Ratio (%) 57.5 55.0 55.1 53.3 Fee Inc / Operating Rev (%) 32.6 29.5 29.1 29.4 Asset Quality NPAs / Loans + OREO (%) 1.62 2.38 0.98 0.76 NCOs / Avg Loans (%) 0.55 1.12 0.32 0.01 Reserves / Loans (%) 1.40 1.46 1.68 2.02 Texas Ratio (%) 7.37 13.37 4.42 3.61 |
 10 Established Presence in Core Markets of Operation Established Presence in Core Markets of Operation American State has significant deposit market share in its markets, including top three rankings in the attractive Lubbock, Abilene and Odessa markets Note: ASFC excludes one drive thru branch in Odessa, eight mobile deposit services for nursing homes that do not retain deposits (seven in Lubbock and one in Abilene) and six branches not defined by an MSA representing $199 million in deposits Represents a top 5 market share Source: SNL Financial and Microsoft MapPoint; Deposit data as of June 30, 2011 American State Deposit Market Share by Texas MSA MSA Market Rank Branch Count Deposits in Market ($mm) Market Share (%) Population 2010 (Actual) Proj. HH Income 2010-15 (%) Lubbock 3 9 737.5 12.2 276,354 15.2 Abilene 2 6 316.5 13.9 161,179 15.6 Odessa 2 4 282.2 12.6 134,891 14.5 Midland 8 2 228.3 4.9 133,025 10.9 Plainview 2 1 125.0 23.5 35,071 12.9 Levelland 3 1 87.4 17.4 22,344 14.9 Snyder 4 1 86.5 22.1 16,060 14.2 Big Spring 5 1 40.2 8.0 33,702 14.8 Brownwood 5 2 29.0 5.5 38,784 14.3 Granbury 8 2 26.3 2.9 61,010 8.4 San Angelo 13 1 19.5 1.1 109,521 14.5 Dallas-Fort Worth 157 1 18.3 0.0 6,540,927 11.5 MSA Totals 31 1,996.7 7,562,868 |
 11 West Texas Markets Economies at a Glance West Texas Markets Economies at a Glance Lubbock MSA Abilene MSA Midland-Odessa “Petroplex” (1) Midland-Odessa combined unemployment rate calculated as a weighted average of Midland and Odessa MSA unemployment rates Source: 2010 Census Bureau, Unemployment rates per Bureau of Labor Statistics as of December 2011 • Population: approximately 275,000; unemployment rate: 5.3% • Serves as the economic, education and health care hub of the South Plains region • Home to Texas Tech University (30,000+ students) and Lubbock Christian University (1,500+) • Largest contiguous cotton-growing region in the world • Population: approximately 160,000; unemployment rate: 6.0% • Home to Dyess Air Force Base, a 6,000 acre military facility home to 13,000 military and civilian people with an annual economic impact of $310 million • Diverse economy, including wind, medical, oil and high tech industries, has stabilized the region and weathered the recession’s regional impact • Combined population: approximately 274,000; unemployment rate: 4.5% (1) • Located on the Permian Basin, a petroleum rich area of West Texas, and home to the New York Mercantile Exchange’s benchmark West Texas Intermediate Crude • Combined economies grew 13.5% in 2011 as high crude prices have driven record consumer spending and a strong housing market |
 12 Pro Forma Loan Composition Pro Forma Loan Composition Prosperity Bancshares, Inc. American State Financial Corporation Pro Forma Loan Portfolio ($000) % of Total Commercial R.E. 1,441,226 $ 38.3% Commercial 439,854 11.7% Construction 482,140 12.8% 1-4 Family Residential 1,007,266 26.7% Consumer 78,187 2.1% Agriculture 170,234 4.5% Home Equity 146,999 3.9% Gross Loans 3,765,906 $ 100.0% Yield on Loans 5.70% Loan Portfolio ($000) % of Total Commercial R.E. 537,051 $ 44.3% Commercial 298,219 24.6% Construction 87,575 7.2% 1-4 Family Residential 172,364 14.2% Consumer 66,944 5.5% Agriculture 42,466 3.5% Home Equity 7,271 0.6% Gross Loans 1,211,890 $ 100.0% Yield on Loans 5.24% Loan Portfolio ($000) % of Total Commercial R.E. 1,978,277 $ 39.7% Commercial 738,073 14.8% Construction 569,715 11.4% 1-4 Family Residential 1,179,630 23.7% Consumer 145,131 2.9% Agriculture 212,700 4.3% Home Equity 154,270 3.1% Gross Loans 4,977,796 $ 100.0% Yield on Loans 5.59% Source: PB’s 4 Quarter 2012 Earnings Release and company documents for American State; Data as of December 31, 2011; Yield on loans as of quarter ended December 31, 2011 Commercial R.E. 38.3% Commercial 11.7% Construction 12.8% 1-4 Family Residential 26.7% Consumer 2.1% Agriculture 4.5% Home Equity 3.9% Commercial R.E. 44.3% Commercial 24.6% Construction 7.2% 1-4 Family Residential 14.2% Consumer 5.5% Agriculture 3.5% Home Equity 0.6% Commercial R.E. 39.7% Commercial 14.8% Construction 11.4% 1-4 Family Residential 23.7% Consumer 2.9% Agriculture 4.3% Home Equity 3.1% th |
 13 Pro Forma Deposit Composition Pro Forma Deposit Composition Prosperity Bancshares, Inc. American State Financial Corporation Pro Forma Deposit Portfolio ($000) % of Total Non-interest Bearing DDA 1,972,226 $ 24.5% Interest Bearing DDA 1,532,701 19.0% MMA & Savings 2,557,023 31.7% CD's & IRA's<100m 968,806 12.0% CD's & IRA's>100m 1,029,498 12.8% Total Deposits 8,060,254 $ 100.0% Cost of Total Deposits 0.44% Deposit Portfolio ($000) % of Total Non-interest Bearing DDA 561,065 $ 22.8% Interest Bearing DDA 574,094 23.3% MMA & Savings 642,744 26.1% CD's & IRA's<100m 249,553 10.1% CD's & IRA's>100m 432,073 17.6% Total Deposits 2,459,529 $ 100.0% Cost of Total Deposits 0.42% Deposit Portfolio ($000) % of Total Non-interest Bearing DDA 2,533,291 $ 24.1% Interest Bearing DDA 2,106,795 20.0% MMA & Savings 3,199,767 30.4% CD's & IRA's<100m 1,218,359 11.6% CD's & IRA's>100m 1,461,571 13.9% Total Deposits 10,519,783 $ 100.0% Cost of Total Deposits 0.44% Non-interest Bearing DDA 24.5% Interest Bearing DDA 19.0% MMA & Savings 31.7% CD's & IRA's<100m 12.0% CD's & IRA's>100m 12.8% Non-interest Bearing DDA 22.8% Interest Bearing DDA 23.3% MMA & Savings 26.1% CD's & IRA's<100m 10.1% CD's & IRA's>100m 17.6% Non-interest Bearing DDA 24.1% Interest Bearing DDA 20.0% MMA & Savings 30.4% CD's & IRA's<100m 11.6% CD's & IRA's>100m 13.9% Source: PB’s 4 Quarter 2012 Earnings Release and company documents for American State; Data as of December 31, 2011; Cost of deposits as of quarter ended December 31, 2011 th |
 14 Capital Ratio Analysis Capital Ratio Analysis (1) (2) ($mm) PB ASFC Pro Forma 12/31/11 12/31/11 9/30/12 Balance Sheet Total Assets 9,823 $ 3,082 $ 13,969 $ Tangible Assets 8,877 3,058 12,743 Risk Weighted Assets 4,357 1,628 6,285 8,784 3,003 12,293 Deposits 8,060 2,460 11,055 Capital Tangible Common Equity 622 256 808 Tier 1 Capital 693 245 880 Total Capital 745 265 933 Capital Ratios TCE / TA 7.0% 8.4% 6.3% Leverage 7.9% 8.1% 7.2% Tier 1 Capital 15.9% 15.0% 14.0% Total Capital 17.1% 16.3% 14.9% Average Assets for Leverage Ratio (1) Estimated close is pro forma for pending and recently completed acquisitions: Texas Bankers, East Texas Financial Services, Bank Arlington, and American State Financial Corporation (2) Calculated as average assets less non-allowable intangibles; per regulatory guidance |
 15 Contact Information Contact Information Corporate Headquarters Investor Contacts Prosperity Bank Plaza David Zalman 4295 San Felipe Chairman & Chief Executive Officer Houston, Texas 77027 979.543.2200 david.zalman@prosperitybanktx.com 281.269.7199 Telephone Dan Rollins 281.269-7222 Fax President & Chief Operating Officer www.prosperitybanktx.com 281.269.7199 dan.rollins@prosperitybanktx.com David Hollaway Chief Financial Officer 281.269.7199 david.hollaway@prosperitybanktx.com |
 ASFC Merger Presentation - 2/27/12 |