The study presents a comprehensive database of the optical properties of 20 different plant-based, synthetic, and mineral oils within the terahertz (THz) radiation range. The analysis focused on the absorption coefficient and refractive index in the frequency range of 100 GHz to 1.5 THz. The optical properties of the oils were measured using terahertz time-domain spectroscopy (THz TDS) with the TeraPulse Lx Modular System (TeraView) operating in transmission mode with a dry-air chamber. Additionally, the database includes results from THz TDS measurements conducted in the 100 GHz to 2 THz range on a multilayer structure with three inlets. These results demonstrate a reduction in signal loss associated with undesired internal reflections within the multilayer structure when a specifically selected synthetic oil was applied for the successive filling of the inlets.