Decommissioned oil tanks offer previously untapped potential for thermal energy storage in industry. At the HACO AG site, three identical underground chambers (approx. 1,150 m³) that formerly stored fossil fuels are being investigated. The aim of the project is to make these volumes usable for the temporary storage of industrial waste heat and renewable heat. The project includes technical, safety-related, and economic feasibility studies, a hydraulic integration study, thermal simulations (Modelica), and the calculation of heat production costs (LCOH). Depending on the utilization concept, around 2.5 GWh of heat per year can be stored at the site and used at a later time. The findings will be published in a transferable, practice-oriented guide for industry.