Abstract Upper Cretaceous depositional-sequence architecture of the Tremp Basin in the Pyrenees reflects the effects of both subsidence and eustasy. Overall geometry is controlled by thermal subsidence, and depositional-sequence geometry, depositional facies, and sequence boundaries are controlled by relative sea-level oscillations as well as subsidence. Five depositional sequences, of seismic stratigraphic scale, are recognized. (A) The three oldest sequences show moderate extent of the bayline coastal onlap, backstepping of each successively younger carbonate platform, and shelfward basin encroachment, which increased the water depth in the basin. (B) The fourth sequence is the thickest sequence and displays a dramatic backstepping of the carbonate platform with coastal onlap occurring over 60 km shelfward of the previous sequences. The fourth sequence is divided into a lower siliciclastic-rich subsequence and an upper carbonate-rich subsequence. Depositional sequences one through four can be divided into a volumetrically small transgressive lower unit and a volumetrically large regressive upper unit. (C) The fifth depositional sequence shows an overall regressive cycle that filled the basin. Two subsequences are differentiated, each made of siliciclastic nearshore, shelf, and basin facies. Sequence boundaries, over most of the study area, are concordant surfaces where a sharp transition from shallower to deeper water facies occurs. These conformable surfaces can be traced (1) shelfward into subaerial karst surfaces, or channelized surfaces filled with sandstone, and (2) basinward into submarine erosional truncations over which chaotic sediments onlap. Tectonism is recorded in the geometry and sequence boundaries of the Upper Cretaceous sediments of the Tremp Basin. Thermal subsidence during Cenomanian-Coniacian time created depositional space in the basin, but uplift and slow-subsidence rates reduced bayline onlap on the shelf. Subsidence increased during late Santonian time, creating new depositional space and a widespread coastal onlap. Uplift concurrent with thrusting during Maastrichtian time induced erosion around the thrust area. Post-thrust crustal relaxation created new depositional space for accumulation of the fifth sequence. The formation of the sequence boundaries was influenced by listric-normal faulting, uplift, and periods of rapid subsidence. Relative sea-level changes of as much as 150 m are recorded in the Upper Cretaceous of the Tremp Basin. Comparison of the sediment thickness with the predicted space created by thermal subsidence requires relative sea-level oscillations to create the additional depositional space needed for sediment accumulation. The geometry of each depositional sequence, with a thin transgressive unit and a thick regressive unit, suggests an initial rapid sea-level rise followed by a stillstand with subsequent sea-level drop toward the end of the sequence. The relative lowering of sea-level exposed the inner shelf, and in some cases channels were cut on the platform and filled with sandstones. However sea-level drops do not appear to have exposed the entire shelf and shelf edge. These sea-level drops may have triggered erosion in the basin by increasing the current activity and instability of sediments. The depositional sequences and sequence boundaries recognized in the Tremp Basin are time equivalent to other sequences and sequence boundaries in other Cretaceous basins. These similarities between different basins support a "global" mechanism controlling depositional sequences during the Upper Cretaceous, with distinctive tectonic factors in each basin (or a segment of a basin) controlling each depositional-sequence geometry and facies pattern and depositional-sequence succession.