Abstract: An improved method for assessing the geologic risk for hydrocarbon presence and hydrocarbon accumulation size is disclosed. In one configuration, seismic attributes are assigned to a horizontal axis and data quality to a vertical axis to form a matrix cross-plot. Direct Hydrocarbon Indicators (DHI) derived from seismic data are used to qualify the presence and accumulation size. A quantitative method for scaling and calibrating the DHI matrix is illustrated that can be applied to existing petroleum basins and by analog to frontier areas.