Existing oil leakage detection approaches on the ocean or on the land have suffered from shortcomings like low-sensitivity, environment-vulnerability and high cost and energy consumption. A unique simple-structured upward open-channel microbial fuel cell (UOC-MFC) was developed to solve these challenges, in which the open-channel rolled cathode vertically floated on the electrolyte solution surface and simultaneously contacted with both air and water. Oil presence covered the cathode surface, blocked the oxygen diffusion on the cathode and thus caused the prompt drop of the potential readings of the UOC-MFC sensors. The oil shock tests using engine oil (EO) showed that the potential decrease and the response time exhibited excellent linear relationships (R2 > 0.99) with the EO amount, indicating a good sensitivity. Due to the separation of the anode and the invading oil, the UOC-MFC sensor recovered its external potential within 2.3 h after the EO shock tests, indicating a good reusability. The power density of the UOC-MFC was 450 mW/m3 under normal condition and dropped to 207 mW/m3 after EO shock due to the internal resistance increasing from 1.29 to 3.80 kΩ. The UOC-MFC integrated with a power management system (PMS) theoretically supported a voltage meter and data transmitter. This study well demonstrated the great potential of the UOC-MFC for in-situ detecting oil presence in a real-time self-sustained mode.