Complex sentence: The oil extraction industry started with the exploitation of the fields in Cheleken in 1909 (by Branobel) and Balkanabat in the 1930s, then production leaped ahead with the discovery of the Kumdag field in 1948 and the Koturdepe field in 1959.
Split into simpler sentences: The oil extraction industry started with the exploitation of the fields in Cheleken in 1909 (by Branobel) and in Balkanabat in the 1930s. Production leaped ahead with the discovery of the Kumdag field in 1948 and the Koturdepe field in 1959.