Optical coherence tomography (OCT) has been introduced for the diagnosis of vulnerable plaques in the coronary arteries. When an OCT system images through tissue and biological liquids, group velocity dispersion (GVD) will occur, which may be useful in tissue characterization. This study compares the water and lipid induced GVD effects, important constituents in plaque, on the axial resolution. The point-spread function (PSF) was measured when a target mirror was immersed in either water or lipid. A Fourier transform was performed on the PSF data. No significant GVD was observed in oil up to 15 mm thickness. Water depths greater than 6 mm significantly broadened the PSF. This indicates that the distortion of the spectrum can be attributed to the GVD in water. These results suggest that when imaging through tissue (such as when performing intravascular imaging in vivo) one may be able to distinguish different tissue types for diagnostic purposes.