Large reserves of oil and gas have been found in rocks of lacustrine origin in Rocky Mountain basins, and these strata remain largely unexplored.

Except for the productive limestone of the Sheep Pass Formation (eastern Nevada), lacustrine carbonate reservoir rocks found to date have poor porosity and permeability. Sandstone is the best reservoir rock of the lacustrine suite.

Most of the productive sandstone beds originated in deltaic complexes. Sandstone bodies paralleling old lake shores are much poorer objectives than their marine counterparts because of lower transport energy and relatively unstable water level in lakes. Large deltaic complexes are prime objectives, and directional criteria can be observed within the lacustrine facies as well as in the equivalent fluvial facies.

The oil- and gas-producing sandstone units of the western Green River basin (commonly interpreted to have originated as beaches and bars along the west shore of a Paleocene-Eocene lake) are almost certainly of fluvial origin. These sandstone beds have no low-energy lateral facies equivalents which are characteristic of lacustrine deposits.

Typically the main body of lacustrine deposits consists of very finely and uniformly laminated, well-indurated shale and very argillaceous microcrystalline carbonate rocks. Brown bituminous shale and oil shale are common. Proximal to the deltaic facies, shale becomes more variable. Induration decreases, sorting decreases, lamination and fissility decrease, siltstone is common, and slump structures and load casts are present in some places.

The distal margins of sandstone bodies are well-cemented, well-sorted, very fine-grained (grading to siltstone), and thinly and horizontally bedded with abundant small ripple marks. They contain abundant shale partings on well-defined bedding planes. The main body of a typical lacustrine sandstone contains well-cemented oolitic laminae and thin beds alternating with thick to massive beds of porous, friable sandstone. Sorting is fair to good. Proximal to the fluvial facies, sandstone beds are poorly sorted with abundant clay matrix in many beds. "Soft" clasts (e.g., shale fragments) are common.

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