Abstract: The invention provides a method for forming particles of a target substance, comprising (a) co-introducing into a particle formation vessel, under controlled temperature and pressure, a supercritical or near-critical anti-solvent fluid; a “target solution or suspension” of the target in a first vehicle; and a second vehicle which is soluble in the anti-solvent fluid; and (b) using the anti-solvent to disperse the target solution/suspension and the second vehicle, and to extract the vehicles, substantially simultaneously and substantially immediately on introduction of the fluids into the particle formation vessel, wherein the second vehicle is immiscible with the first, and wherein contact between the target solution/suspension and the second vehicle occurs a sufficiently short period of time before their dispersion by the anti-solvent, and with sufficient physical mixing, as to allow only insignificant, if any, phase separation to occur between the two vehicles between their contact with one another and thei