Chromium incorporation into TiO 2 up to 3GPa at 1300°C and 900°C has been studied by XRD as well as TEM. A CaCl 2 type TiO 2 polymorph has been observed in the quenched samples from high pressure. Two different mechanisms of solubility occur in the recovered samples. Chromium replaces titanium on normal octahedral sites but it also occupies interstitial octahedral sites, especially in the samples recovered from higher pressures. Interstitial chromium is responsible for an orthorhombic distortion of the TiO 2 rutile structure in the quenched samples and gives rise to a (110) twinned CaCl 2 -structured polymorph. This phase is very likely the result of temperature quench at high pressure. The formation of this phase is directly related to the chromium content of the TiO 2 grains. Chromium solubility in TiO 2 increases with increasing the synthesis pressure. TiO 2 is able to accommodate up to 15.3wt% Cr 2 O 3 at 3GPa and 1300°C, compared to 5.7wt% at atmospheric pressure at the same temperature.