Although most bacteria produce fatty acids (FA), few secrete free FAs into the culture media. Over-expression of two FA thioesterases, TesA and AtFatA, facilitated both total and FFA production in a recombinant strain of Escherichia coli. When these thioesterases were expressed in a fadD and fadL double-deletion strain, a further enhancement of FFA secretion was observed. These results support a simple diffusion mechanism for FA transport. In addition, the ATP-binding cassette transporter protein, MsbA, also increased the concentration of FFAs in the culture. The final strain produced 110 mg FFA/l, about 33 % of the total FAs being produced. Our findings support a diffusion mechanism for FA transport.