<p>The effects of pressure and the action of metal oxide microparticles on the composition and rheological properties of the liquid products of the low‑temperature cracking of a high‑viscosity oil from the Ashalchinsky deposit at 360°C were studied. The contents of resinous‑asphaltene compounds and of the low‑boiling fraction IBP‑200°C in the products are greater than in the starting oil and increase when the process is carried out with increasing pressure up to 10 MPa. These findings suggest the importance of condensation processes. In comparison, when using microparticles of Al₂O₃, ZnO, and Fe₂O₃, the contents of resins and low‑boiling fractions remain almost unchanged, while the content of asphaltenes decreases and the amount of saturated hydrocarbons increases in the low‑temperature cracking products at pressure 10 MPa. The conversion of asphaltenes increases to 30% in the cracking of heavy oil in a subcritical aqueous fluid at a pressure of 18 MPa with the addition of Fe₂O₃ microparticles. These changes in the composition of the cracking products lead to a significant decrease in the viscosity anomaly indices and to a drop in the viscosity of the products by 42‑52% in comparison with the initial oil sample. The specific features of the composition of low‑temperature cracking products that affect their rheological properties should be taken into account when developing technologies for preparing high‑viscosity heavy oil for transport and subsequent refining.</p>