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Alcanivorax borkumensis, a marine bacterium highly specialized in degrading linear and branched alkanes, plays a key ecological role in the removal of marine oil spills. It contains several alternative enzyme systems for terminal hydroxylation of alkanes, including three P450 cytochromes (P450‐1, P450‐2 and P450‐3). The present work shows cytochrome P450‐1 to be expressed from the promoter of the upstream gene fdx. Promoter P_fdx was more active when C₈‐C₁₈ n‐alkanes or pristane were assimilated than when pyruvate was available. The product of ABO_0199 (named CypR) was identified as a transcriptional activator of P_fdx. The inactivation of cypR impaired growth on tetradecane, showing the importance of the fdx‐P450‐1 and/or cypR genes. P450‐2 expression was low‐level and constitutive under all conditions tested, while that of P450‐3 from promoter P_450‐3 was much higher when cells …