The Denver basin covers some 58,000 square miles in portions of Colorado, Wyoming, South Dakota, Nebraska, and Kansas, and is directly related to the series of intermontane basins developed in the Rocky Mountain mobile belt during the Laramide revolution. Although preponderantly of Cretaceous age, sediments in the Denver basin range from Cambrian to Recent, and attain a maximum thickness of 15,000 feet along the westerly asymmetric flank of the basin. Although attention was focused on the area as early as 1862 with the discovery of oil in the Canon City, Colorado, area, the current heightened activity stems from the discovery of significant reserves of Cretaceous oil in the Nebraska portion of the basin during 1949. Two productive horizons have been defined; the sands of he Cretaceous Dakota group account for the great bulk of the production, and the Permian Lyons sand is currently productive in but two fields. With the general absence of significant structural closure, stratigraphic traps assume the primary role. The considerable random drilling encouraged by low well costs has largely masked the material contribution made by scientific methods, but an alliance of these two exploratory approaches has greatly accelerated the development of the basin. The cumulative production to July 1954 was 51,382,000 barrels. The estimated reserve of 87,000,000 barrels at the end of 1953 was at least doubled by drilling during 1954, attesting to the youthful stage of exploratory development in the basin.