A mechanistic study on the oligomerization of olefins of isomeric octenes using a Lewis-acidic ionic liquid as the catalyst is reported herein. This study was aimed at understanding the effects of the position and geometry of the double bond on the probable pathway of the reaction and the properties of the final product. This effort will help in understanding which feed or mixture of feeds can be used as starting materials for oligomerization and also in understanding and estimating the final product properties after oligomerization. We observed an interesting reactivity pattern in the oligomerization of a mixture of olefins, in which there is selectivity for the cis isomer over the trans isomer. In addition, we found that the final oligomer obtained starting from a mixture of olefin isomers displayed better properties, such as a higher viscosity index and a lower side-chain branching percentage, than that obtained starting from exclusively the alpha-olefin. Kinetic studies were carried out with individual isomers of octenes and their mixtures toward oligomerization. Subsequently, analyses of the structural properties of the final oligomerized and hydrogenated products were undertaken.