An engineered thioesterase enzyme which converts a C10, C12 or C14 acyl-ACP substrate to a fatty acid derivative with a greater activity as compared to the wild-type thioesterase having the amino acid sequence presented as SEQ ID NO:31, wherein the engineered thioesterase (a) is derived from a precursor thioesterase comprising an amino acid sequence that is at least 90% identical to SEQ ID NO:31; and (b) has a substitution corresponding to a substitution selected from: i) D45A, D45C, D45E, D45F, D45G, D45H, D45I, D45K, D45L, D45M, D45P, D45Q, D45S, D45T, D45V, D45W; ii) N73A, N73C, N73G, N73H, N73I, N73L, N73P, N73R, N73S, N73T, N73V, N73W; iii) G78A, G78C, G78D, G78E, G78F, G78M, G78N, G78P, G78Q, G78R, G78S, G78T, G78V, G78Y; iv) Q80A, Q80E, Q80G, Q80L, Q80M, Q80S, Q80W, Q80Y; v) E101A, E101D, E101G, E101L, E101M, E101P, E101S, E101T, E101V; vi) R108A, R108C, R108D, R108E, R108F, R108G, R108H, R108I, R108L, R108M, R108R, R108S, R108V, R108W, R108Y; vii) A111C, A111E, A111L, A111M, A111N, A111P, A111Q, A111R, A111S, A111V, A111W, A111Y; viii) Y117A, Y117C, Y117D, Y117E, Y117G, Y117H, Y1171, Y117L, Y117M, Y117N, Y117P, Y117Q, Y117R, Y117S, Y117T, Y117V, Y117W; ix) N118A, N118C, N118E, N118F, N118G, N118H, N118I, N118K, N118L, N118M, N118P, N118Q, N118S, N118T, N118V, N118W; x) S122A, S122C, S122D, S122E, S122F, S122G, S122I, S122L, S122M, S122P, S122R, S122V, S122W, S122Y; xi) Y145A, Y145C, Y145D, Y145E, Y145G, Y145I, Y145L, Y145M, Y145N, Y145Q, Y145R, Y145S, Y145T, Y145W; xii) Q152A, Q152D, Q152E, Q152F, Q152H, Q152I, Q152K, Q152L, Q152N, Q152R, Q152S, Q152T, Q152V, Q152Y; xiii) V178A, V178F, V178G, V178L, V178R, V178S, V178T, V178W; in SEQ ID NO:31, wherein methionine is at position 0 and alanine is at position 1 of SEQ ID NO:31. (a) is derived from a precursor thioesterase comprising an amino acid sequence that is at least 90% identical to SEQ ID NO:31; and (b) has a substitution corresponding to a substitution selected from: i) D45A, D45C, D45E, D45F, D45G, D45H, D45I, D45K, D45L, D45M, D45P, D45Q, D45S, D45T, D45V, D45W; ii) N73A, N73C, N73G, N73H, N73I, N73L, N73P, N73R, N73S, N73T, N73V, N73W; iii) G78A, G78C, G78D, G78E, G78F, G78M, G78N, G78P, G78Q, G78R, G78S, G78T, G78V, G78Y; iv) Q80A, Q80E, Q80G, Q80L, Q80M, Q80S, Q80W, Q80Y; v) E101A, E101D, E101G, E101L, E101M, E101P, E101S, E101T, E101V; vi) R108A, R108C, R108D, R108E, R108F, R108G, R108H, R108I, R108L, R108M, R108R, R108S, R108V, R108W, R108Y; vii) A111C, A111E, A111L, A111M, A111N, A111P, A111Q, A111R, A111S, A111V, A111W, A111Y; viii) Y117A, Y117C, Y117D, Y117E, Y117G, Y117H, Y1171, Y117L, Y117M, Y117N, Y117P, Y117Q, Y117R, Y117S, Y117T, Y117V, Y117W; ix) N118A, N118C, N118E, N118F, N118G, N118H, N118I, N118K, N118L, N118M, N118P, N118Q, N118S, N118T, N118V, N118W; x) S122A, S122C, S122D, S122E, S122F, S122G, S122I, S122L, S122M, S122P, S122R, S122V, S122W, S122Y; xi) Y145A, Y145C, Y145D, Y145E, Y145G, Y145I, Y145L, Y145M, Y145N, Y145Q, Y145R, Y145S, Y145T, Y145W; xii) Q152A, Q152D, Q152E, Q152F, Q152H, Q152I, Q152K, Q152L, Q152N, Q152R, Q152S, Q152T, Q152V, Q152Y; xiii) V178A, V178F, V178G, V178L, V178R, V178S, V178T, V178W; in SEQ ID NO:31, wherein methionine is at position 0 and alanine is at position 1 of SEQ ID NO:31. i) D45A, D45C, D45E, D45F, D45G, D45H, D45I, D45K, D45L, D45M, D45P, D45Q, D45S, D45T, D45V, D45W; ii) N73A, N73C, N73G, N73H, N73I, N73L, N73P, N73R, N73S, N73T, N73V, N73W; iii) G78A, G78C, G78D, G78E, G78F, G78M, G78N, G78P, G78Q, G78R, G78S, G78T, G78V, G78Y; iv) Q80A, Q80E, Q80G, Q80L, Q80M, Q80S, Q80W, Q80Y; v) E101A, E101D, E101G, E101L, E101M, E101P, E101S, E101T, E101V; vi) R108A, R108C, R108D, R108E, R108F, R108G, R108H, R108I, R108L, R108M, R108R, R108S, R108V, R108W, R108Y; vii) A111C, A111E, A111L, A111M, A111N, A111P, A111Q, A111R, A111S, A111V, A111W, A111Y; viii) Y117A, Y117C, Y117D, Y117E, Y117G, Y117H, Y1171, Y117L, Y117M, Y117N, Y117P, Y117Q, Y117R, Y117S, Y117T, Y117V, Y117W; ix) N118A, N118C, N118E, N118F, N118G, N118H, N118I, N118K, N118L, N118M, N118P, N118Q, N118S, N118T, N118V, N118W; x) S122A, S122C, S122D, S122E, S122F, S122G, S122I, S122L, S122M, S122P, S122R, S122V, S122W, S122Y; xi) Y145A, Y145C, Y145D, Y145E, Y145G, Y145I, Y145L, Y145M, Y145N, Y145Q, Y145R, Y145S, Y145T, Y145W; xii) Q152A, Q152D, Q152E, Q152F, Q152H, Q152I, Q152K, Q152L, Q152N, Q152R, Q152S, Q152T, Q152V, Q152Y; xiii) V178A, V178F, V178G, V178L, V178R, V178S, V178T, V178W;