X0306 4 2020-03-12 0001624322 Business First Bancshares, Inc. BFST 0001734773 MANSFIELD KEITH 500 LAUREL STREET, SUITE 101 BATON ROUGE LA 70801 1 EVP&COO of b1Bank COMMON STOCK 2020-03-12 4 P 0 2000 15.85 A 21095 D This transaction was executed in multiple trades at prices ranging from $15.845 to $15,8478. The price reported above reflect the weighted average sale price. The reporting person hereby undertakes to provide upon request to the SEC staff, the issuer or a security holder of the issuer full information regarding the number of shares and prices at which the transaction was effected. Includes (a) 755 shares of unvested restricted stock granted on 03/31/2018 and (b) 1,292 shares of unvested restricted stock granted on 03/31/2019, in each case subject to vesting in three equal installments over a period of two years beginning on the grant date and subject to the terms of the relevant restricted stock grant. The reported shares of unvested restricted stock are subject to forfeiture upon the occurrence of certain events specified in the restricted stock grant. Includes 5,000 shares held by reporting person's IRA. /s/ Heather Roemer, as attorney-in-fact for Keith Mansfield 2020-03-13