Thirty four shale samples from the Tertiary Agbada Formation were analysed for TOC and Rock-Eval pyrolysis parameters in order to evaluate the effect of oil-based mud contamination on source-rock characterization. The samples were obtained from five wells in the offshore Niger Delta over a depth range of 5,460ft to 11,580ft. The results indicated that the raw (unextracted) samples were dominated by Type III kerogen. However, after extraction, both Types II/III and III kerogen were identified, consistent with previous studies. These results demonstrate that it is essential that shale samples should be extracted prior to TOC and Rock-Eval pyrolysis for accurate source-rock evaluation.