The Yegua Formation (Late Middle Eocene) is a minor siliciclastic progradation of the Gulf of Mexico shelf margin between the larger Early Eocene and Oligocene shelf-margin progradations. During Yegua time (and unlike the other units of the Middle and Late Eocene), four to eight sea-level fluctuations with a 100-300 ka period alternately pushed marine rocks toward the basin margins and pushed deltaic sedimentation to and past the shelf edge. Because of limited to moderate sand supply and the flat coastal plains, the updip (highstand) depositional complexes are nearly entirely separated from the downdip (lowstand) shelf-edge deltas and slope fans. Maximum flooding surfaces can be mapped over much of the area and correlated along and across the basin. The Yegua is truly a laboratory for sequence stratigraphy. A number of plays in the downdip and 'mid-dip' (incised valley complexes) trends have produced over 4 TCF of gas and condensate, and new discoveries await the return of exploration capital. The Yegua story is significant to all those interested in siliciclastic stratigraphy in passive-margin settings.