Surface seeps first attracted industrial exploration for hydrocarbons in Sicily in 1901. The first major success occurred after passage of the Sicilian petroleum law of 1950. Three major structural accumulations have been discovered--Ragusa (1953), Gela (1956), and Gagliano (1960). Recoverable reserves are estimated to be 110 million bbl at Ragusa and 90 million bbl at Gela. Although oil in place at Gela is calculated to be 1.3 billion bbl, less than 10 percent is expected to be recovered. At Gagliano, proved reserves are not defined fully, although about 700 billion ft³ (20 billion m³) of gas and 20 million bbl of condensate are estimated. Development drilling is still under way at Gagliano and Gela.

Commercial production is limited to the Tertiary Central basin and the Mesozoic Ibleo platform. The Central basin is characterized by a thick sequence of normally deposited Pliocene and Miocene terrigenous clastic rocks interspersed with chaotic gravitational slides. The Gagliano field produces from multipay Miocene-Oligocene sandstone beds. The Ibleo platform is represented primarily by carbonate rocks, and the Ragusa and Gela fields produce from thick dolomite of Triassic age.

Volcanic activity which began in the Jurassic has continued to the present, and intrusive rocks commonly are associated with the producing reservoirs.