So far, the understanding of Pre-Tertiary formations in the Phu Quoc basin is eliminated due to lack of drilling and the absence of outcrops except on Phu Quoc Island and some other isles. By analogue with stratigraphic information from surrounding areas, seismic horizons may be correlated with known-age strata. Strata of pre-Cambrian and Early Paleozoic ages have not been discovered yet in SW Viet Nam but by analogue may consist of metamorphosed rocks such as chloritized phylite, sericite schist, and quartzite sandwiched with ultra basic rocks. Therefore, PetroVietnam assigned PVEP to perform acquisition of 2D seismic on the area of blocks 41- 44 in order to get additional data for more precise evaluation of the petroleum potential and defining the exploration strategy in the Phu Quoc area.Based on seismic data interpretation in block 42 of Phu Quoc Basin, the Isodepth maps were constructed by approach of conversingtime to depth from isochrone maps. The results of interpretation allowed to identify many seismic closures particularly on the isodepth map of the Brown section, but these closures are located deeply above 5000m, which reliability is fair and economic effect is weak. Hence, the Brown horizon did not considered as structures identified on and concentrate to describe those determined in the Orange and Purple horizons. Result of interpretation indicated 8 closures, which could be identified in the Orange and Purple horizons

New exploration results proved the presence of Tertiary sedimentary basins with hydrocarbon potential in the boundaries of Vietnam continental shelf. These basins were perhaps formed in the Early Oligocene on the Mesozoic basement of continental crust and were filled with mainly deltaic clastic sediments. Since very early Miocene these basins have linked together and extended wider. Sediments of marine and prograding delta facies accumulated and widespreaded on the whole continental shelf. At the Middle Miocene to present-day the opening of the Bien Dong Sea (Vietnam East Sea), the regional tectonic subsidence and the eustatic fluctuation had created sedimentary formations of open and deep marine facies with turbidite shale, platform carbonate including reef build-up. Andesite and basalt extrusion occurred in form of dykes resulting from tectonic inversions in Late Oligocene, in the beginning of Middle Miocene, particularly in Late Miocene-Pliocene. These Tertiary sedimentary basins are expected to have hydrocarbon potential and need to be investigated and explored adequately. The main risk is the drilling technology, the exploitation in the deep sea and high investment cost. The recently exploration results in illustrated a better potential in Lower Oligocene reservoir in South East margin of Cuu Long basin and many new signs. These signs need to be highlight researched for predicting accumulation distribution in study area, in purpose of oil and gas exploration for next stages.