Sea-level fluctuations due to changing mid-ocean ridge volumes have been calculated for the last 80 m.y. in 5-m.y. intervals. An analysis of the errors involved in this set of calculations includes: the effect of omitting calculations for crust more than 70-m.y. older than the ridge crest at any given time; inaccurate estimates of stage poles and ridge lengths; subducted ridges for which only a remnant triple junction remains; completely subducted ridges; and uncertainty in absolute dating of magnetic anomalies. The maximum possible sea level 80 m.y. ago was 365 m (1,198 ft); the minimum was 45 m (148 ft) with a most probable height of about 230 m (755 ft) above present sea level. A decrease in spreading rates since the Late Cretaceous was the primary cause of a volume decrease in mid-ocean ridges.