X0306 4 2020-03-13 0001624322 Business First Bancshares, Inc. BFST 0001734794 MOCKLER PATRICK E. 500 LAUREL STREET, SUITE 101 BATON ROUGE LA 70801 1 COMMON STOCK 2020-03-13 4 P 0 3000 14.45 A 12473 D This transaction was executed in multiple trades at prices ranging from $14.3989 to $14.45. 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. /s/ Heather Roemer, as attorney-in-fact for Patrick E. Mockler 2020-03-17