This work deals with the hydrothermal liquefaction of biomass, especially suspensions of microalgae. The goal of this approach is to produce a “bio-crude”, which can be utilized in conventional crude-oil refineries. At the beginning, a literature review of the state-of-the-art in the field of hydrothermal liquefaction of microalgae was conducted, at which continuous and discontinuous processes are distinguished. A consideration of catalysts and their effects related to hydrothermal liquefaction supplemented this research. Special attention is paid on natural genesis of crude oil deposits and the examination of potential cross-links to the technical process of hydrothermal liquefaction by investigating physicochemical conversion and transport processes during the formation of natural crude oil. Information about process parameters, mineralogy and conversion reactions are combined and discussed. In two series of experiments technical process parameters and catalysts are investigated. Therefore, a 600 ml autoclave in batch mode is used. Temperatures from 275 to 350 °C were examined. Moreover, different strains of algae (Spirulina and Scenedesmus) are compared. Montmorillonite and ZSM-5 zeolites are used as heterogeneous catalysts. The resulting "bio-crude" as well as the produced gases during HTL are characterized by quantitative and qualitative analyses (elemental composition, heating values, GC-MS, gas analysis by FTIR, mass balances). The determined bio-crude yield was up to 45 % of the dried algal biomass and maximum heating values of up to 44.5 MJ/kg were obtained.