In geology we often revise theoretical models; upon finding new evidence,such as the discovery of methane hydrates, the initial model will be challenged immediately. Hereby the authors put forward two postulates:1) There is a third, previously unexplored source of methane in the Transylvanian Basin, based on a new theoretical approach on methane hydrate formation; 2) The dissociation of methane hydrates creates a strong chlorinity anomaly. Based on a recent analogy with the Black Sea basin model, we apply our statements to the Transylvanian Basin. Using direct and indirect indicators and the published system tract analysis, we claim that there are substantial grounds to believe that this model of methane hydrate formation applies to the Miocene Transylvanian Basin. Due to the increase of the geothermal gradient as a result of the volcanic activity from the Eastern Carpathians, the clathrates dissociated into methane and freshwater. This process of dilution resulted in a chlorinity anomaly that can be spotted in the formation waters of several gas fields from the Transylvanian Basin.