The Sunnyside oil-impregnated sandstone deposit is a giant, exhumed oil field which occurs in the Green River Formation (Eocene), southwestern Uinta basin, Utah. The updip limit of the deposit has been eroded; thus, the precise mechanism of entrapment cannot be determined.

The deposit occurs within a transgressive continental and lacustrine sequence. The alluvial Colton Formation (early Eocene) underlies the deposit and grades into marginal lacustrine strata of the overlying Green River Formation. The lower part of the marginal lacustrine sequence is predominantly deltaic, but the upper third is interbedded with open lacustrine facies. The uppermost part of the Green River Formation in the area is eroded.

Petroleum-impregnated sandstone beds occur throughout the approximately 1,370 ft (418 m) of exposed marginal lacustrine facies. However, the main part of the deposit has a gross oil column of at least 860 ft (270 m) of which 640 ft (195 m) are petroleum-saturated siliciclastic rocks.

The deposit is exposed only on the southwest side and at the northwest corner. Only 12 significant wells were drilled in an area of 20 sq mi (52 sq km) prior to 1979. Thus, the limits of the deposit and the contained petroleum resource are difficult to assess. The delineated part of the deposit contains about 2.2 billion bbl of petroleum in place. The downdip limit of the deposit has not been defined.

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