The local registry and orientation of chemisorbed 3-methylthiophene and 3-methoxythiophene on Cu(111) has been determined using normal incidence X-ray standing wavefield absorption and near edge X-ray absorption fine structure spectroscopy, respectively. 3-methylthiohene and 3-methoxythiophene have, within experimental error, identical local registries (atop), Cu-S separations (2.57 +/- 0.03 and 2.55 +/- 0.05 Angstrom). and orientations (24 +/- 4 degrees and 26 +/- 4 degrees). These results are placed in context with previous studies of thiophene and 3-chlorothiophene and provide quantitative information on how simple substituents affect the adsorption structure of the thiophene ring.