Compaction of sedimentary rocks over basement hills was first recognized as a cause of structural closure in 1919. In the ensuing decade, many leading petroleum geologists espoused and expanded the concept to include compaction over hills on unconformity surfaces higher in the sedimentary section, compaction over sand buildups within the sedimentary section, and compaction over carbonate reefs. However, following the initial flurry of interest, compaction as a cause of structure was relegated to a minor role in petroleum exploration or was dismissed altogether by most workers. In 1983, studies undertaken at Applied Geophysics, Inc., indicated that many oil fields on structural closure in Oklahoma and Kansas coincided with basement fault blocks deduced from high-resolution residual aeromagnetics. A literature search, followed by a geological library search for closely spaced basement penetrations in the Mid-continent, has located 30 basement hills, all of which show structural closure in the overlying sedimentary rocks. One must conclude that compaction as a cause of structure is a pervasive geological phenomenon. Additional findings of the ongoing study have been that (1) thinning over structural highs can be explained by compaction of lower beds surrounding basement hills while the overlying strata were being deposited, that is, by syndepositional compaction, (2) flank fracturing can result by compaction over dense underlying hills if lithification takes place prior to deposition of overlying beds, (3) crestal porosity on compaction structures can result when deposition proceeds slower than compactional settling, (4) salt domes may be localized over the top of compaction structures, and (5) much "tectonic" disturbance is not tectonic at all but is the result of compactional tilting followed by erosion and deposition of flat beds over the tilted ones on the flanks of compaction structures.