Exposure of the unsymmetrical spiroalkanedithiol, 2-octyl-2-pentadecylpropane-1,3-dithiol, to the surface of gold afforded a multicomponent self-assembled monolayer (SAM) in which the differing tail groups were well mixed at the molecular level. The new "mixed" SAM was characterized by ellipsometry, contact angle goniometry, polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS), and atomic force microscopy (AFM). Comparison of the new SAM to those generated by the coadsorption of mixtures of normal alkanethiols having analogous chain lengths and surface compositions showed that local domain formation (or "islanding") of the tail groups found in the latter SAMs was absent in the SAM derived from the unsymmetrical spiroalkanedithiol.