A dual riser FCC process is disclosed wherein first and second hydrocarbon feeds (5, 6) are supplied to the respective first and second risers (2, 4) to make an effluent rich in ethylene, propylene and/or aromatics. Where the hydrocarbon feeds are different, the respective risers can have different conditions to favor conversion to ethylene and/or propylene. A minor amount of a coke precursor (80, 82) can be added to one or both of the hydrocarbon feeds (5, 6) to reduce or eliminate the amount of supplemental fuel needed to heat balance the system. The different feeds, including the coke precursor and any recycle streams (36, 44) can be segregated by type to improve olefin yields, including an embodiment where the paraffinic feeds are supplied to one riser and the olefinic feeds to the other.