Undewater natural gas pipelines whose numbers and ages are increasing day by day can be punctured because of various reasons. In this study, nature of acoustic signals generated by leakages on pipelines is examined and a novel passive acoustic based system is proposed to detect the acoustic signals remotely, determine size of the leak hole and estimate approximate distance of the leakage. The method is examined by executing some numerical studies. In these numerical studies offshore part of Maghreb-Europe gas (MEG) pipeline which is still in use is used as an example. Obtained results revealed that the leakages can be detected from tens of kilometers. Localization of the leakage is also possible by combining proposed method with appropriate methods in literature.