A process for producing a hydrocarbon composition that comprises contacting a feed stream, that comprises at least one C.sub.3 to C.sub.8 olefin, and an olefinic recycle stream, that comprises a first olefinic recycle stream and no more than 10 wt % of C.sub.10+ non-normal olefins, with a molecular sieve catalyst in a reaction zone under olefin oligomerization conditions producing an oligomerization effluent stream; separating the oligomerization effluent stream to produce a first olefinic stream, that has a weight ratio of C.sub.4-/(C.sub.5-C.sub.8) molecules from about 0.8 to about 1.2 times the weight ratio of C.sub.4-/(C.sub.5-C.sub.8) molecules found in the oligomerization effluent stream, and a first hydrocarbon product stream, that comprises at least 1 wt % and no more than 30 wt % of C.sub.9 non-normal olefin; and splitting the first olefinic stream to produce the first olefinic recycle stream and a first purge stream.