A process for catalytic conversion of low value hydrocarbon streams to light olefins in comparatively higher yields is disclosed. Propylene is obtained in amounts higher than 20 wt. % and ethylene higher than 6 wt. %. The process is carried out in a preheated cracking reactor having a single riser and circulating an FCC catalyst. The riser is divided into three temperature zones in which different hydrocarbon feeds are introduced. An oxygenate feed is introduced in the operative top zone in the riser. Heat for the endothermic cracking is obtained by the exothermic reaction of converting the oxygenate feed into gas and/or from a regenerator in which the spent FCC catalyst is burnt.