Olefin oligomerization to produce hydrocarbon compositions useful as fuels

A process for producing a hydrocarbon composition, the process comprising:

• (a) contacting a feed comprising at least one C3 to C8 olefin and an olefinic recycle stream rich in C9− hydrocarbons with a crystalline molecular sieve catalyst having an average crystal size no greater than 0.15 micron and an alpha value between about 100 and about 600 in at least one reaction zone under olefin oligomerization conditions including an inlet temperature between about 180° C. and about 340° C., a pressure of at least 2,860 kPa and a recycle to feed weight ratio of about 0.1 to about 3.0, said contacting producing a oligomerization effluent stream;
• and
• (b) separating said oligomerization effluent stream into at least a hydrocarbon product stream rich in C9+ hydrocarbons and said olefinic recycle stream.