SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 11-K (X) ANNUAL REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended December 31, 1998 OR ( ) TRANSITION REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to . Commission file number 0-12508 A. Full title of the plan and the address of the plan, if different from that of the issuers named below: S&T BANCORP, INC., THRIFT PLAN FOR EMPLOYEES OF S&T BANK B. Name of issuer of the securities held pursuant to the plan and the address of its principle executive office: S&T BANCORP, INC. 800 PHILADELPHIA STREET INDIANA, PA 15701 Thrift Plan for Employees of S&T Bank Financial Statements Years ended December 31, 1998 and 1997 Contents Report of Independent Auditors.................................. 	1 Audited Financial Statements Statements of Net Assets Available for Benefits................. 	2 Statements of Changes in Net Assets Available for Benefits...... 	4 Notes to Financial Statements................................... 	6 Line 27a-Schedule of Assets Held for Investment Purposes........	12 Line 27d-Schedule of Reportable Transactions....................	14 Report of Independent Auditors Thrift and Retirement Plan Committee S&T Bank We have audited the accompanying statements of net assets available for benefits of the Thrift Plan for Employees of S&T Bank as of December 31, 1998 and 1997, and the related statements of changes in net assets available for benefits for the years then ended. These financial statements are the responsibility of the Plan's management. Our responsibility is to express an opinion on these financial statements based on our audits. We conducted our audits in accordance with generally accepted audit- ing standards. Those standards require that we plan and perform the audit to obtain reasonable assurance about whether the financial statements are free of material misstatement. An audit includes examining, on a test basis, evidence supporting the amounts and disclosures in the financial statements. An audit also includes assessing the accounting principles used and significant estimates made by management, as well as evaluating the overall financial statement presentation. We believe that our audits provide a reasonable basis for our opinion. In our opinion, the financial statements referred to above present fairly, in all material respects, the net assets available for benefits of the Plan at December 31, 1998 and 1997, and the changes in its net assets available for benefits for the years then ended, in conformity with generally accepted accounting principles. Our audits were performed for the purpose of forming an opinion on the financial statements taken as a whole. The accompanying supple- mental schedules of assets held for investment purposes as of December 31, 1998, and reportable transactions for the year then ended, are presented for purpose of additional analysis and are not a required part of the financial statements, but are supplementary information required by the Department of Labor's Rules and Regulations for Reporting and Disclosure under the Employee Retirement Income Security Act of 1974. These supplemental schedules are the responsibility of the Plan's management. The Fund Information in the statements of net assets avail- able for benefits and the statements of changes in net assets available for benefits is presented for purposes of additional analysis rather than to present the net assets available for benefits and the changes in net assets available for benefits of each fund. The supplemental schedules and Fund Information have been subjected to the auditing procedures applied in our audits of the financial statements and, in our opinion, are fairly stated in all material respects in relation to the financial statements taken as a whole. June 11, 1999 1 Thrift Plan for Employees of S&T Bank Statement of Net Assets Available for Benefits with Fund Information December 31, 1998 [CAPTION] Bank Money Diversified Fixed Vanguard Special ESOP ESOP Mass Stock Market Equity Income Index 500 Growth Alloc- Suspense Mutual Fund ated Fund Total Cash $ 2,942 $ 385 $ 3,308 $ 1,504 $ 710 $ 335 $- $ - $- $ 9,184 Investments: Short-term investment funds 185,001 1,424,218 23,397 37,594 4,118 2,259 - 10,008 - 1,686,595 Mutual funds - - 4,889,982 2,575,748 816,878 330,295 - - - 8,612,903 S&T common stock 25,247,846 - - - - - - 1,069,444 - 26,317,290 25,432,847 1,424,218 4,913,379 2,613,342 820,996 332,554 - 1,079,452 - 36,616,788 Receivables: Transfer receivable (payable) 1,007,854 - - - - - - (1,007,854) - - Accrued interest and dividends 165,653 6,096 103 141 649 20 - 7,824 - 180,486 Payables: Refund of excess advance return to Plan Sponsor - - - - - - - 79,422 - 79,422 - - - - - - - 79,422 - 79,422 Net assets available for benefits $26,609,296 $1,430,699 $4,916,790 $2,614,987 $822,355 $332,909 $- $ - -$36,727,036 See accompanying notes. 2 Thrift Plan for Employees of S&T Bank Statement of Net Assets Available for Benefits with Fund Information December 31, 1997 [CAPTION] Mass Bank Money Diversified Fixed ESOP ESOP Mutual Stock Market Equity Income Allocated Suspense Funds Total Cash $ 449,011 $ 5,231 $ 52,428 $ 12,687 $ 33,256 $ 2,500 $ - $ 555,113 Investments: Short-term investment funds 17,454 623,477 435,592 71,104 5,210 - 149,792 1,302,629 Mutual funds - - 2,717,705 2,234,042 - - 637,435 5,589,182 Common stock of S&T Bancorp, Inc. 10,572,938 - - - 11,428,985 562,250 - 22,564,173 10,590,392 623,477 3,153,297 2,305,146 11,434,195 562,250 787,227 29,455,984 Receivables: Accrued interest and dividends 73,658 2,962 336 318 79,362 6,963 - 163,599 Payables: Note payable to bank - - - - - 130,000 - 130,000 Payable to participant for overfunding 3,979 592 4,659 10,629 - - - 19,859 3,979 592 4,659 10,629 - 130,000 - 149,859 Net assets available for benefits $11,109,082 $631,078 $3,201,402 $2,307,522 $11,546,813 $441,713 $787,227 $30,024,837 See accompanying notes. 3 Thrift Plan for Employees of S&T Bank Statement of Changes in Net Assets Available for Benefits with Fund Information Year ended December 31, 1998 [CAPTION] Mass Bank Money Diversified Fixed Vanguard Special ESOP ESOP Mutual Stock Market Equity Income Index 500 Growth Fund Allocated Suspense Funds Total Additions: Contributions: Employer (participant accounts) $ 144,715 $ 17,486 $ 168,807 $ 44,217 $18,135 $ 9,374 $ 2,967 $393,078 $ - $ 798,779 Employee- payroll 377,148 42,092 442,448 115,536 50,262 26,066 - - - 1,053,552 Employee- rollover 42,224 2,118 26,029 15,855 11,265 1,023 - - - 98,514 564,087 61,696 637,284 175,608 79,662 36,463 2,967 393,078 - 1,950,845 Investment income: Dividends 396,684 73,791 265,011 164,404 4,547 11,731 230,363 21,316 279 1,168,126 Assets trans- ferred from the Peoples Bank of Unity 401(k) plan Deductions: Distributions to participants (1,318,600) (144,144) (205,487) (61,514) (1,802) (776) (995,257) - (10,776) (2,738,356) Payment of interest on note payable - - - - - - - (9,548) - (9,548) Expenses - - - - - - - - (2,074) (2,074) Transfer of assets 12,956,482 808,278 724,533 19,750 664,797 331,622(13,722,952)(1,007,854) (774,656) - Net realized gains and unrealized appreciation (depreciation) in aggregate fair value of investments 2,901,561 - 294,047 9,217 75,151 (46,131) 2,938,066 161,295 - 6,333,206 Net additions (deductions) 15,500,214 799,621 1,715,388 307,465 822,355 332,909 (11,546,813) (441,713) (787,227) 6,702,199 Net assets available for benefits at beginning of year 11,109,082 631,078 3,201,402 2,307,522 - - 11,546,813 441,713 787,227 30,024,837 Net assets available for benefits at end of year $26,609,296 $1,430,699 $4,916,790 $2,614,987 $822,355 $332,909 $ - $ - $ - $36,727,036 See accompanying notes. 4 Thrift Plan for Employees of S&T Bank Statement of Changes in Net Assets Available for Benefits with Fund Information Year ended December 31, 1997 [CAPTION] Mass Bank Money Diversified Fixed ESOP ESOP Mutual Stock Market Equity Income Allocated Suspense Funds Total Additions: Contributions: Employer (participant accounts) $ 255,965 $ 18,959 $ 165,598 $ 50,559 $ 500,000 $ - $ - $ 991,081 Employee-payroll 316,110 41,506 424,081 133,314 - - 5,544 920,555 Employee-rollover 69,523 18,960 46,829 7,141 - - - 142,453 641,598 79,425 636,508 191,014 500,000 - 5,544 2,054,089 Investment income: Dividends 274,566 31,339 469,964 141,241 288,256 25,985 7,416 1,238,767 Assets transferred from the Peoples Bank of Unity 401(k) plan - - - - - - 982,346 982,346 Deductions: Distributions to participants (326,764) (19,118) (117,851) (95,178) (351,199) - (313,351) (1,223,461) Payment of interest on note payable - - - - - (16,816) - (16,816) Expenses - - - - - - (1,500) (1,500) Refunds (3,979) (592) (4,659) (10,629) - - - (19,859) Transfer of assets 501,567 (1,050) (60,211) (101,399) 508 (339,415) - - Net realized gains and unrealized appreciation in aggregate fair value of investments 2,929,699 - 108,268 27,175 3,172,876 287,500 106,772 6,632,290 Net additions (deductions) 4,016,687 90,004 1,032,019 152,224 3,610,441 (42,746) 787,227 9,645,856 Net assets available for benefits at beginning of year 7,092,395 541,074 2,169,383 2,155,298 7,936,372 484,459 - 20,378,981 Net assets available for benefits at end of year $11,109,082 $631,078 $3,201,402 $2,307,522 $11,546,813 $441,713 $787,227 $30,024,837 See accompanying notes. 5 Thrift Plan for Employees of S&T Bank Notes to Financial Statements December 31, 1998 1. Summary of Significant Accounting Policies A description of significant accounting policies of the Thrift Plan for Employees of S&T Bank (the Plan) is presented below. Trusteed Assets The investment assets are held in trust with the Trust Department of S&T Bank and Massachusetts Mutual Life Insurance Company (Mass Mutual) (collectively, the Trustees). Mass Mutual was the trustee for the Peoples Bank of Unity Plan which merged into the S&T Plan on May 9, 1997. Mass Mutual was a trustee of a portion of the plan assets until January 5, 1998 at which time all assets were held with the Trust Department of S&T Bank. Valuation of Investments Marketable securities are stated at fair value. Securities traded on a national securities exchange are valued at the last reported sales price on the last business day of the plan year; investments traded in the over-the-counter market and listed securities for which no sale was reported on that date are valued at the average of the last reported bid and asked prices. The fair value of participation units in the short- term investment funds and mutual funds was based on quoted redemption values at cost which approximates fair value. Realized Gains and Losses Realized gains and losses from investment transactions are computed principally using the first-in, first-out (FIFO) method. Use of Estimates The preparation of financial statements in conformity with generally accepted accounting principles requires management to make estimates that affect the amounts reported in the financial statements and accompanying notes. Actual results could differ from those estimates. 2. Description of the Plan The Plan was adopted effective May 1, 1984 and made retroactive to January 1, 1984 by S&T Bank (Plan Sponsor and Employer). 6 Thrift Plan for Employees of S&T Bank Notes to Financial Statements (continued) 2. Description of the Plan (continued) The Plan is a vehicle for accepting employee and employer tax-deferred contributions and employee after-tax contributions. Eligible employees (participants) determine the amount of their deferred cash contributions to the Plan. Employer Matching contributions are equal to 50% of the employee contributions, not to exceed 3% of compensation. Employer Additional contributions are determined by the Board of Directors of the Plan Sponsor. The Plan was amended, effective December 30, 1988, to include an Employee Stock Ownership Plan (ESOP). The ESOP covers substantially all regular employees under the Plan. ESOP contributions are invested primarily in qualified securities (common stock) of S&T Bancorp, Inc. (Bancorp), the parent company of the Plan Sponsor. In conjunction with the creation of the ESOP, the Trustee acquired 560,000 shares of Bancorp common stock (as restated to reflect two-for-one stock splits on June 12, 1992, September 15, 1994 and October 30, 1998) with the proceeds of a promissory note (Note) for $2,800,000 dated December 31, 1988 payable by the Plan to a bank not affiliated with the Plan Sponsor. The shares of Bancorp common stock are pledged as security on the Note. The Note requires quarterly interest and annual principal payments beginning in 1989 and has a maximum term of ten years and a minimum term of seven years and bears interest at 80% of the lender's prime rate. Bancorp has guaranteed the Note, and the Plan Sponsor is obligated to make annual contributions sufficient to fund principal amortization and interest payments on the Note, net of investment income in the ESOP Suspense Fund. Shares released from the collateral pledge during the years ended December 31, 1998 and 1997, totaled 26,000 and 20,000 as a result of principal payments made during the years of $130,000 and $100,000, respectively. At December 31, 1998, there were no unreleased shares as the Plan Sponsor paid all outstanding principal on the loan during 1998. Effective October 1, 1998, the Plan was amended and restated to permit eligibility to participate in the Plan upon employment with S&T Bancorp. The Plan was also amended to include automatic participation of eligible participants unless participants elect otherwise. The Plan added the Vanguard Index 500 Fund and Special Growth Fund as new investment options. The Plan was also amended to comply with the Small Business Job Protections Act of 1996 and the Taxpayer Relief Act of 1997. Individual accounts are maintained for each participant. Participants may elect to invest their contributions in one or more of the following funds: Bank Stock Fund, Money Market Fund, Diversified Equity Fund, Fixed Income Fund, Vanguard Index 500 Fund, or Special Growth Fund. The Employer contributions are invested at the direction of the Thrift and Retirement Plan Committee of the Plan Sponsor. 7 Thrift Plan for Employees of S&T Bank Notes to Financial Statements (continued) 2. Description of the Plan (continued) At December 31, 1997, the Plan also held investments in six Mass Mutual funds as a result of the merger of the Plan with the Peoples Bank of Unity 401(k) Savings Plan on May 9, 1997. All investments merged from the Peoples Bank of Unity 401(k) Savings Plan remained in the Mass Mutual investments through the remainder of the Plan's year. All employees of Peoples Bank of Unity were eligible to participate upon the merger of the Plan on May 9, 1997. Effective January 5, 1998, all assets invested in Mass Mutual funds were liquidated and transferred in the investment options available under the Plan according to the participants' elections. Each participant's account is credited with the participant's contributions, Employer Matching contributions and allocations of other Employer contributions and fund earnings, which are allocated based on the participant's compensation and the participant's fund balances, respectively. The benefit to which a participant is entitled is the amount aggregated in the participant's account. Aggregate participant account balances differ from net assets available for benefits only by routine accruals and the unallocated balance of the ESOP Suspense Fund. Participants are immediately vested in all amounts credited to their accounts. On termination of service, participants may elect either to receive a lump-sum distribution from their accounts, or to leave their funds in the Plan, provided their balance is at least $5,000. The Plan Sponsor reserves the right to amend or discontinue the Plan. In the event of a termination of the Plan, plan assets would be used for the benefit of participants and their beneficiaries, as prescribed by law. For more complete information about the Plan including participation, vesting, and benefit provisions, refer to the Summary Plan Description, which can be obtained from the Plan Sponsor. 8 Thrift Plan for Employees of S&T Bank Notes to Financial Statements (continued) 3. Investments During 1998 and 1997, the Plan's investments (including investments purchased and sold, as well as held during the year) appreciated in fair value by $6,333,206 and $6,632,290, respectively, as follows: Net Appreciation (Depreciation) in Fair Value for Year Ended December 31 1998 1997 Mutual funds $ 332,284 $ 242,215 Common stock of S&T Bancorp, Inc. 6,000,922 6,390,075 $6,333,206 $6,632,290 The fair value of individual investments that represent 5% or more of the Plan's net assets available for plan benefits is as follows: December 31 1998 1997 S&T Bancorp, Inc.-common stock $26,317,290 $22,564,173 All investment information disclosed in the accompanying financial statements and schedules in total and by fund, including investments held at December 31, 1998 and 1997, and net appreciation/depreciation in fair value of investments, interest, and dividends for the years ended December 31, 1998 and 1997, were obtained or derived from information supplied to the plan administrator and certified as complete and accurate by the trustees. 4. Transactions with Parties-in-Interest Legal, accounting, and other administrative fees are paid by the Plan Sponsor. The Plan is administered by the Plan Sponsor, and the Trust Department of S&T Bank acts as trustee and safekeeping agent. At December 31, 1998 and 1997, respectively, the Plan held an aggregate of 954,805 and 1,043,430 shares (as restated for a two-for-one stock split effective October 30, 1998) of S&T Bancorp, Inc. common stock valued at $26,317,290 and $22,564,173. 9 Thrift Plan for Employees of S&T Bank Notes to Financial Statements (continued) 4. Transactions with Parties-in-Interest (continued) During February 1998, S&T Bancorp made a tender offer to purchase a portion of its outstanding shares. Shares held by participants in the Plan were eligible for the tender offer. As a result of the tender offer, S&T Bancorp purchased 62,456 shares (as restated for a two-for-one stock split effective October 30, 1998) from participants of the Plan at a price of $24.50 per share resulting in proceeds of $1,530,172. The proceeds from the sale of shares were placed into the Plan in the individual participants' accounts who participated in the tender offer. 5. Income Tax Status The Plan has received a determination letter from the Internal Revenue Service dated November 20, 1995, stating that the Plan is qualified under Section 401(a) of the Internal Revenue Code of 1986 (the Code) and that the trust, therefore, is exempt from taxation under Section 501(a) of the Code. Once qualified, the Plan is required to operate in conformity with the Code and the Employee Retirement Income Security Act of 1974 to maintain its tax-exempt status. The Plan was amended on October 1, 1998, subsequent to the IRS determination letter. The Plan has applied for but has not received a determination letter from the Internal Revenue Service stating that the amended Plan is qualified under the Code. However, the Plan administrator believes that the Plan is qualified and, therefore, the related trust is exempt from taxation. 6. Year 2000 (Unaudited) The Year 2000 issue is the result of computer programs having been written using two digits rather than four to define the applicable year. This could result in a system failure or miscalculations causing disruptions of Plan operations, including, among other things, a temporary inability to process transactions or engage in normal Plan activities. The Plan Sponsor has determined that it will be necessary to take certain steps in order to ensure that the Plan's information systems are prepared to handle Year 2000 dates. The Plan Sponsor's approach to the Year 2000 issue addresses both internal systems and third party service providers and consists of four phases: assessment, remediation, testing and implementation. Both internal and external resources are being utilized to replace or modify existing software applications, and test the software and equipment for the Year 2000 modifications. The Plan Sponsor anticipates substantially completing all phases of the project relating to its internal systems during the first half of 1999. Total costs associated with modifying the Plan Sponsor's software and equipment are estimated to be approximately $300,000 and will be paid by the Plan Sponsor. 10 Thrift Plan for Employees of S&T Bank Notes to Financial Statements (continued) 6. Year 2000 (Unaudited) (continued) The Plan Sponsor also established formal communications with its third party service providers to determine that they have developed plans to address their own Year 2000 problems as they related to the Plan's operations. The Plan Sponsor converted to the third party's Year 2000 compliant software during the fourth quarter of 1998. The Plan Sponsor's management has developed contingency plans to address internal systems, applications and third party service providers. The contingency plans involve alternative processing plans in the event of system or application failure. The Plan Sponsor finalized the contingency plans during the first half of 1999. The Plan Sponsor's management believes that all of the Plan's systems will be Year 2000 ready. 11 Thrift Plan for Employees of S&T Bank EIN-25-0776600 Plan-002 Line 27a-Schedule of Assets Held for Investment Purposes December 31, 1998 [CAPTION] Description of Investment, Including Maturity Date, Rate of Identity of Issuer, Borrower, Interest, Collateral, Current Lessor or Similar Party Par or Maturity Value Cost Value ESOP Suspense Fund Federated Prime Obligations Fund 10,008 units $ 10,008 $ 10,008 S&T Bancorp, Inc.* 38,800 shares of common stock 478,150 1,069,444 488,158 1,079,452 Bank Stock Fund Federated Prime Obligations Fund 185,001 units 185,001 185,001 S&T Bancorp, Inc.* 916,005 shares of common stock 7,478,223 25,247,846 7,663,224 25,432,847 Money Market Fund Federated Prime Obligations Fund 1,424,218 units 1,424,218 1,424,218 Diversified Equity Fund Federated Prime Obligations Fund 23,397 units 23,397 23,397 Emerging Markets Fund 17,049 units 172,483 144,575 Real Estate Securities Fund 7,909 units 217,619 193,304 Quantitative Equity Fund 32,105 units 1,113,948 1,364,768 Diversified Equity Fund 27,596 units 1,184,562 1,418,695 International Securities Fund 9,541 units 558,326 580,647 Equity Income Fund 10,555 units 429,359 435,508 Special Growth Fund 17,362 units 730,037 752,485 4,429,731 4,913,379 * Indicates party-in-interest to the Plan 12 [CAPTION] Line 27a-Schedule of Assets Held for Investment Purposes (continued) Description of Investment, Including Maturity Date, Rate of Identity of Issuer, Borrower, Interest, Collateral, Current Lessor or Similar Party Par or Maturity Value Cash Value Fixed Income Fund Federated Prime Obligations Fund 37,594 units 37,594 37,594 Volatility Constrained Bond Fund 52,412 units 994,859 1,004,743 Diversified Bond Fund 66,766 units 1,521,665 1,571,005 2,554,118 2,613,342 Vanguard Index 500 Fund Federated Prime Obligations Fund 4,118 units 4,118 4,118 Vanguard Index 500 Fund 7,169 units 740,483 816,878 744,601 820,996 Special Growth Fund Federated Prime Obligations Fund 2,259 units 2,259 2,259 Special Growth Fund 7,621 units 376,545 330,295 378,804 332,554 Total assets held for investment purposes $17,682,854 $36,616,788 13 Thrift Plan for Employees of S&T Bank EIN-25-0776600 Plan-002 Line 27d-Schedule of Reportable Transactions Year ended December 31, 1998 [CAPTION] Current Value of Asset on Purchase Selling Cost of Transaction Net Gain Description of Assets Price Price Asset Date or (Loss) Type (I) Transactions-Individual transactions of the same issue in excess of 5 % of the fair value of plan assets S&T Bancorp, Inc. Sale of 31,228 shares $ - $1,530,172 $ 529,961 $1,530,172 $1,000,211 Federated Prime Obligations Fund Purchase of 1,530,173 units 1,530,172 - 1,530,172 1,530,172 - Purchase of 1,572,622 units 1,572,622 - 1,572,622 1,572,622 - Sale of 1,566,221 units - 1,566,221 1,566,221 1,566,221 - Type (III) Transactions-Series of transactions of the same issue aggregating in excess of 5% of the fair value of plan assets S&T Bancorp, Inc. 12 purchases 953,480 - 953,480 953,480 - 23 sales - 2,007,176 742,975 2,007,176 1,264,201 Federated Prime Obligations Fund 348 purchases 8,783,499 - 8,783,499 8,783,499 - 218 sales - 8,248,941 8,248,941 8,248,941 - There were no Type (II) or (IV) reportable transactions during 1998. 14 SIGNATURES The Plan. Pursuant to the requirements of the Securities Exchange Act of 1934, the trustees (or other persons who administer the employee benefit plan) have duly caused this annual report to be signed on its behalf by the undersigned hereunto duly authorized. Thrift Plan for Employees for S&T Bank June 29, 1999 /s/ Robert E. Rout Executive Vice President & Chief Financial Officer