Low-moleculuar-weight hydrogenated oligomers prepared from middle-range (C,-C,,J I-olefins are finding increasing importaince as synthetic lubricating fluids. For this reason, it is desirable to understand both the mechanism by which they form and their structure. The accepted mechanisms and structures associated with cationic potymerization of olefins are not consistent with the physical and chemical properties of oligomers formed by BF, catalysis. In addition, conventional theories of the mechanism do not explain the unique product distribution resulting from these reactions. We propose and present evidence for a skeletal rearrangement through a protonated cyclopropane intermediate during the course of the oligomerization reaction. This explains many apparent anomalies both in the behavior of these reactions and in the properties of the resulting products.