The surface compositions of bisphenol A polycarbonate and poly(dimethylsiloxane) (BPAC-PDMS) random block copolymers were analyzed using angle-dependent electron spectroscopy for chemical analysis (ESCA) and attenuated total reflection (ATR) FTIR. The composition tvas measured at sampling depths of 18, 73, and 103 Angstrom with angle-dependent ESCA and at a sampling depth of 4.1 mu m with ATR-FTIR. The present study focuses on examining the quantitative effects of solvent casting and annealing on the surface composition of the BPAC-PDMS random block copolymers of varying bulk compositions. The effects of solvent casting were evaluated in terms of solvent solubility (or Hildebrand parameter) and solvent volatility (or boiling point). It was found that the casting solvents and annealing treatments influenced the surface compositions significantly, and each of the solvents gave the polymer film a different morphology in the near surface region. In addition, a physical picture of the near surface region (103 Angstrom) of siloxane block copolymers cast from selected solvents is compared to the thicker region (similar to 4.1 mu m) probed by ATR-FTIR.