Interaction between basement subsidence, eustatic sea-level changes, and varying sediment supply shapes the sediment accumulations along passive continental margins. Detailed analysis of the sediments with seismic stratigraphy and well data permits quantification of the subsidence history and reconstruction of paleoenvironments and sea-level changes through time. Geohistory analysis provides a quantitative analysis of basin subsidence using geologic time-depth diagrams to visualize the total basin subsidence. Long-term eustatic changes are a significant component of the thermo-tectonic subsidence curve. These changes can be quantified by measuring dpearture from an established set of calculated subsidence curves. Short-term, rapid changes of sea level can be demonstrated from seismic and well data. The stratigraphic resolution of these changes rarely allows exact quantification of their magnitude, but a minimum rate of change of sea level can often be determined. Applications of these procedures are demonstrated with an example from northwest Africa.