A continuous technique for upgrading light olefinic crackate gas from hydrocarbon cracking comprising methods and means for: (a) compressing and cooling a first portion of the light crackate gas to provide a first pressurized ethene-rich vapor stream and a first condensed crackate stream rich in C.sub.3.sup.+ aliphatics; (b) contacting said first ethene-rich vapor stream under pressure with a C.sub.5 + liquid sorbent stream in a gas-liquid contact absorber column under sorption conditions to selectively absorb a major amount of C.sub.3.sup.+ components; (c) recovering a second ethene-rich vapor stream overhead from the absorber column; (d) converting said second ethene-rich vapor stream in a reaction zone in once-through contact with a fluidized bed of said medium pore zeolite catalyst solid particles under oligomerization conditions to produce an olefinic hydrocarbon effluent stream rich in C.sub.5 + hydrocarbons; (e) cooling and separating the reaction effluent stream to provide a light offgas stream and a condensed liquid hydrocarbon product stream; (f) fractionating the condensed liquid hydrocarbon product stream in the absorber column concurrently with sorption of the first ethene-rich vapor stream for recovery of liquid hydrocarbon product with an absorber bottoms liquid stream rich in C.sub.3.sup.+ components; (g) further fractionating the absorber bottoms liquid stream to provide a C.sub.3 -C.sub.4 product and a liquid hydrocarbon fraction consisting essentially of C.sub.5.sup.+ hydrocarbons; (h) recycling at least a portion of the C.sub.5.sup.+ liquid hydrocarbon fraction to the absorber column as the liquid sorbent stream; and bypassing a second portion of said light crackate gas around said absorber to the reaction zone for conversion concurrently with said second ethene-rich vapor stream.