In the area of Northern Adriatic Neogene and Quaternary sediments have relatively large thicknesses. Those are deposited in some depressions located inside Adriatic Basin, where is the largest Po Depression. Recent borders of Po Depression are located in Italian and Croatian offshore where hemipelagic sequences of Pliocene and Pleistocene were interrupted by Po palaeodelta progradations, and to a lesser extent of Adige and Piave Rivers. These sediments include important reservoirs with significant quantities of hydrocarbon gas, and it is why they are well explored in areas of Italian and Croatian gas fields by deep wells as well as different methods for subsurface imaging, mostly by reflective seismic. Sequence of Pliocene and Pleistocene sediments can reach thickness of 6 000 m, and it is divided in lithostratigraphic system with units in rank of formation. On Italian side Cenozoic sediments up to Mesozoic basement are divided in twelve formations, but on Croatian side has been described only one formation. It is Susak Formation that encompasses all Cenozoic rocks. It is why in Croatian part of Northern Adriatic in proposed introducing of the following lithostratigraphic units 8in rank of formation): Dinaridi Formation (Mesozoic rocks), Susak Formation (Palaeocene-Miocene rocks), Istra Formation (Pliocene sediments) and Ivana Formation (Pleistocene and Holocene sediments).