A process for the fluid catalytic cracking of mixed hydrocarbon feeds from different sources is described, such as feeds A and B of different crackability, the process being especially directed to obtaining light fractions such as LPG and comprising injecting feed A in the base of the riser reactive section and feed B, of lower crackability, at a height between 10% and 80% of the riser, with feed B comprising between 5% and 50% of the total processed feed. The process requires that the feeds present differences in the contaminant content, improved dispersion of feeds A and B and feed B injection temperature same or higher than that of feed A.