Tofino Basin comprises a Tertiary forearc assemblage of clastics sediments in excess of four kilometres thick that occupies an area of about 7500 km(2) on the continental margin of western Vancouver Island. The strata are a deep water succession of poorly indurated, interbedded light- to dark-coloured mudstones, siltstones and fine-grained sandstones that have accumulated over the easterly subducting Juan de Fuca Plate. The strata are characterized by an overall low total organic carbon content (avg. = 0.8%) and low hydrogen index (avg. = 80 mg HC/g TOC). The organic matter is predominately Type III and petrographically is comprised mainly of finely divided vitrinite. The richest source rocks are Miocene and Oligocene strata encountered in the D-14 and I-87 wells, but even these are poor source rocks as traditionally defined. Pliocene and younger strata are immature with respect to the oil window, whereas Lower Miocene and Oligocene strata (in the I-87, I-65 drill holes) are mature. Based on a geohistory/maturation model the thermal maturity of the strata is consistent with heat flows in the order of 50 mWm(-2) and thermal conductivity of about 2.0 Wm(-1)K(-1). Such values are similar to modern values in Tofino Basin. Tofino Basin has little liquid hydrocarbon potential as reflected in the overall low total organic carbon content, low hydrogen indexes, petrographic composition of the organic matter and moderate to low maturation gradients.