One or more oligomers of an olefin are prepared in the presence of a single-site catalyst. Preferably, the olefin is an .alpha.-olefin, and the oligomers are a poly-alpha-olefin (PAO). The PAO so prepared is completely or substantially free of tertiary hydrogen resulting from isomerization. Consequently, the PAO possesses improved biodegradability, improved oxidation resistance, and/or a relatively higher viscosity index. The PAO has many useful applications, such as a component of a lubricant.