In the 1970s and 1980s exploration performed within the Polish part of the Permian Basin, particularly in the Gorzow region, found the Main Dolomite (the Upper Permian-Zechstein) formation to be very prospective, as proved by the discovery of many oil and gas fields. In the early 1990s exploration based on 2D seismic intensified and resulted in the definition of three separate structures: Barnowko, Mostno and Buszewo. The exploration wells located on these structures found the first two to be gas-bearing and the third to be oil-filled. Subsequent interpretation of the 3D seismic showed that, in reality, the three discoveries are a single field. This conclusion was based on the analysis of geometry and distribution of the reservoir parameters. It has been proved by the results of eleven consecutive wells (since writing this paper a further 6 wells have been drilled which confirm the interpretation). All of the above shows this field to be the largest oil field of the Polish part of the Permian Basin, as well as the largest in Poland.