The shallower oil and gas reservoir have already been explored and produced. The oil business is forced to drill deeper into the earth's crust. The four ultra-deep wells which reached the third floor of the Vienna Basin are the subject of this thesis. The objective of this thesis is to list and discuss the experiences made at the ultra-deep wells. Furthermore it is important which experiences are relevant for future projects. Beside the drilling aspects it’s important to understand the geology and the structure of the Vienna Basin and so to identify high pressure zones. The challenges of ultra-deep vertical wells – which are significant different from horizontal wells – are discussed. The main drilling principle has not change for years but many drilling techniques have been improved or new developed. These subjects are discussed, too. The experiences from the late 1970s and early 1980s should help to plan future ultra-deep drilling projects. The obtained data should demonstrate the expected incidents and help to avoid mistakes and critical situations.