A feed mixture comprising at least one C.sub.3 olefin and/or at least one C.sub.4 olefin may be contacted with a zeolite catalyst under oligomerization reaction conditions to form a product mixture comprising a plurality of olefin oligomers. The zeolite catalyst, optionally with one or more further modifications, may be selected for operability at high WHSV values that may produce at least C.sub.12 olefins in the product mixture having an average branching index of about 2.2 or less. Under suitable conditions, C.sub.10-C.sub.13 olefins may comprise at least about 25% of the product mixture, M based on total olefin oligomers. Percentage conversion of the at least one C.sub.3 olefin and/or at least one C.sub.4 olefin may impact the average branching index of at least C.sub.12 olefin oligomers and selectivity for C.sub.10-C.sub.13 olefin oligomers. An amount of C.sub.4 olefin in the feed mixture may produce a targeted selectivity for at least C.sub.1 olefins.