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Abstract Microbial flooding is a new enhanced‐oil‐recovery technology for the petroleum industry. In this study, a strain of Bacillus subtilis named SL‐2 was isolated from oil‐well‐produced fluid. B. subtilis produces the lipopeptide surfactin. The fermentation broth of B. subtilis contains lipopeptide biosurfactants (1.2 g/L) with good surface and interfacial activities. Adding 7% of this fermentation broth to water reduces its surface tension from 72 to 33.9 mN/m and the interfacial tension between hexadecane and water from 40 to 1 mN/m. Environmental adaptability analysis revealed that the lipopeptide biosurfactants can tolerate a salinity of 50 g/L NaCl and a temperature of 120°C, and that they have a strong emulsifying effect on the oil phase as well as good emulsification stability owing to their high interfacial shear viscosity. Water contact angle measurements showed that this fermentation broth changes the wettability properties of rock surfaces from hydrophobic to hydrophilic. A new bio‐oil‐displacement system was developed by combining the lipopeptide fermentation broth with xanthan gum, a biopolymer with viscosifying properties. The new bio‐oil‐displacement system has the dual functions of improving oil‐displacement efficiency and expanding sweep volume. The results of laboratory simulation experiments revealed that the oil recovery for a bio‐composite system containing 7% lipopeptide fermentation broth is 18.7% higher than that for water flooding. Therefore, the system has good field application potential. Direct preparation of the oil‐displacement system using the lipopeptide fermentation liquid can reduce the purification cost of the biosurfactant lipopeptide, which is economically conducive to the application of this bio‐oil‐displacement technology.