We report low-rate dynamic contact angle data of various liquids on self-assembled monolayers (SAMs) of octadecanethiol on annealed and nonannealed gold. It was found that interpretation of solid surface tensions using contact angle data on less well-prepared polycrystalline nonannealed gold surfaces can be misleading. Our findings were supported by reflectance infrared spectra and atomic force microscopy data that the surface nanostructure, defects, and polycrystallinity can be important factors for a systematic study of wettability on SAMs in terms of surface energetics. We found that the contact angle and adhesion patterns of various liquids on SAMs of octadecanethiol adsorbed onto annealed gold substrates are consistent with recent experimental data for the relatively thick polymer-coated surfaces. The variation of surface structure in terms of surface energetics can be estimated only when a fundamental understanding of contact angles and surface tensions is known. We estimated an increase in the solid-liquid interfacial tension of 12.9 mJ/m(2) for water on octadecanethiol SAM/nonannealed Au from that of an annealed Au due to structural differences.