Hydrocracking is a second catalytic cracking process applied typically to the heavy vacuum gas oil, a sidecut from the vacuum distillation column. When the oil is mixed with hydrogen and passed over a catalyst, the long chain hydrocarbon molecules are broken down into shorter ones. The rate of cracking and the end products of the hydrocracking are strongly dependent on the temperature and the catalysts present. In Hydrotreatment, a similar cracking process (already described in Section 4.3), the hydrogen is used to break the C-S and C-N bonds: in Hydrocracking the desired break is in the C-C bonds, and the major products are usually jet fuel and diesel. Hydrocracking is therefore used in areas where there is a large demand for diesel fuel. Where the major market demand is for gasoline (petrol) the fluid catalytic cracking process (FCC) is more common.