Integration of gas oil and light olefin catalytic cracking zones with a pyrolytic cracking zone to maximize efficient production of petrochemicals is disclosed. Integration of the units in parallel allows production of an overall product stream with maximum ethylene and/or propylene by routing various feedstreams and recycle streams to the appropriate cracking zone(s), e.g. ethane/propane to the steam pyrolysis zone and C.sub.4 C.sub.6 olefins to the light olefin cracking zone. This integration enhances the value of the material balances produced by the integrated units.