The PANG0001 well is situated at the Claromecó Basin (Buenos Aires Province, Argentina) and it is composed by rocks that belong to the Tunas Formation (Permian, Harrington 1947). It is composed of fine to medium sandstones interbedded with black and gray mudrocks. Coal and black carbonaceous mudstones beds are also interbedded, up to 3 m thick. In these last ones, a petrographic analysis was carried out, in order to determine the type of coal, its depositional environment and its rank (or maturation level), which allowed us to know the oleogenetic potential and the diagenesis level reached by the Tunas Formation. The coals are composed by monomaceralic bands of collovitrinite and gelovitrinite, belonging to vitrinite group and bands of fusinite, belonging to inertinite group. The original environment corresponds to a swamp forest, with alternating wet and dry periods. The vitrinite reflectance shows values from 1.3 to 2.4 %. These values allow classifying the coals as low volatile bituminous to semi-anthracitic. It can be concluded that the formation reached the oil window for condensate and wet gas to methane gas, in a mesogenetic to late mesogenetic stage into the diagenesis.