A process for producing olefins from a feedstock comprising a petroleum and non-petroleum fraction has been developed. The process comprises first pretreating the feedstock to remove contaminants such as alkali metals and then cracking the purified feedstock in a fluidized catalytic cracking (FCC) zone operated at conditions to provide C2-C5 olefins. Alternatively, the non-petroleum fraction can first be treated and then mixed with petroleum fraction to provide the feedstock which is then catalytically cracked.