In our daily life, we are aware that liquid and its vapour can coexist. As we increase the temperature and pressure, however, there is a point called the critical point where the phase boundaries vanish. The temperature and the pressure at the critical point are called critical temperature and critical pressure. Once the temperature and pressure of a system are above its critical values, it is called supercritical fluid and exhibits properties that are between of gas and liquid. These properties have led to enormous applications including production of essential oils and pharmaceutical products, green chemistry, nuclear reactors and formation of nano- and micro-particles. The project aims to be the first joint systematic experimental and theoretical study of the effect of mass and concentration in the microscopic structure and molecular motion in binary supercritical mixtures.