An oil leakage detector for detecting the leakage of e.g. diesel or fuel oil in an engine room of a vessel comprises a conduit for an airflow therethrough, and a screen in the conduit. The screen is meshed to prevent oil particles or droplets from passing therethrough. A sensor determines a pressure loss across the screen, and a control system operatively connected to the sensor is configured to output an oil leakage warning signal if the pressure loss exceeds a predetermined threshold value. A fan may be provided for generating the airflow through the conduit. A gas sensor for determining the presence of hydrocarbon, carbon monoxide or carbon dioxide is optionally provided.