Two oil samples from the Birkhead Formation oil reservoir in Spencer 3 and Spencer 4, and five sidewall cores taken from the Bulldog Shale, Murta Member, Hutton Sandstone, Poolowanna Formation and Patchawarra Formation in Spencer 3 were subjected to detailed organic geochemical analysis, with the following aims: 1. Screen sidewall cores for staining by migrated hydrocarbons; 2. Construct a methylphenanthrene index (MPI) vs depth profile for Spencer 3; 3. Calibrate the MPI against vitrinite reflectance (VR) using existing VR data from Spencer 3; 4. Compare the aromatic and biomarker (sterane, terpane) maturity indices of the oils and rock extracts; 5. Compare the source-dependent biomarker parameters of the oils and rock extracts; and 6. Establish oil-source correlations. Two sidewall core samples from the Murta and Poolowanna formations were found to contain migrated hydrocarbons. The aromatic maturity of the remaining 3 sidewall cores was found not to increase systematically with depth. MPI readings converted to calculated VR values agree only in one case with measured VR. The author concludes that the Birkhead paraffinic oils have similar MPI-derived maturities and are probably of intra-Jurassic origin, but also possess subtle source-related differences.