Pressurised differential scanning calorimetry has been used to study the effects of sand particle size, pressure and oxygen partial pressure on the heat evolution during combustion of North Sea crude/sand mixtures. Both low (LTO) and high temperature oxidation (HTO) regions were identified for all measurements. Decreasing particle size of the sand ana increased pressure increased the extent of LTO and thus favoured fuel lay down. Increase of oxygen concentration increased the heat evolved up to 50% oxygen; further increases in oxygen level had no effect.