Tight oil is a light crude oil contained in petroleum-bearing formations of relatively low porosity

Porosity

Porosity or void fraction is a measure of the void spaces in a material, and is a fraction of the volume of voids over the total volume, between 0–1, or as a percentage between 0–100%...

 and permeability (shale

Shale

Shale is a fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments of other minerals, especially quartz and calcite. The ratio of clay to other minerals is variable. Shale is characterized by breaks along thin laminae or parallel layering...

s). It uses the same horizontal well

Directional drilling

Directional drilling is the practice of drilling non-vertical wells. It can be broken down into three main groups: Oilfield Directional Drilling, Utility Installation Directional Drilling Directional drilling (or slant drilling) is the practice of drilling non-vertical wells. It can be broken down...

 and hydraulic fracturing

Hydraulic fracturing

Considerable controversy surrounds the current implementation of hydraulic fracturing technology in the United States. Hydraulic fracturing, or fracking, is the process of utilizing pressurized water, or some other liquid, to fracture rock layers and release petroleum, natural gas, or other...

 technology used in recent boom in production of shale gas

Shale gas

Shale gas is natural gas produced from shale. Shale gas has become an increasingly important source of natural gas in the United States over the past decade, and interest has spread to potential gas shales in the rest of the world...

. It should not to be confused with oil shale

Oil shale

Oil shale, an organic-rich fine-grained sedimentary rock, contains significant amounts of kerogen from which liquid hydrocarbons called shale oil can be produced...

 and shale oil

Shale oil

Shale oil, known also as kerogen oil or oil-shale oil, is an unconventional oil produced from oil shale by pyrolysis, hydrogenation, or thermal dissolution. These processes convert the organic matter within the rock into synthetic oil and gas...

 as it differs by the API gravity

API gravity

The American Petroleum Institute gravity, or API gravity, is a measure of how heavy or light a petroleum liquid is compared to water. If its API gravity is greater than 10, it is lighter and floats on water; if less than 10, it is heavier and sinks...

 and viscosity

Viscosity

Viscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity...

 of the fluids, as well as the method of extraction.

Tight oil formations include the Bakken Shale, the Niobrara Formation

Niobrara Formation

The Niobrara Formation, also called the Niobrara Chalk , is a geologic formation in North America that was laid down between 87 and 82 million years ago during the Coniacian, Santonian, and Campanian ages of the Late Cretaceous. It is composed of two structural units, the Smoky Hill Chalk Member...

, Barnett Shale

Barnett Shale

The Barnett Shale is a geological formation located in the Bend Arch-Fort Worth Basin. It consists of sedimentary rocks of Mississippian age in Texas...

, and the Eagle Ford Shale in the United States, R'Mah Formation in Syria

Syria

Syria , officially the Syrian Arab Republic , is a country in Western Asia, bordering Lebanon and the Mediterranean Sea to the West, Turkey to the north, Iraq to the east, Jordan to the south, and Israel to the southwest....

, Sargelu Formation in the northern Persian Gulf

Persian Gulf

The Persian Gulf, in Southwest Asia, is an extension of the Indian Ocean located between Iran and the Arabian Peninsula.The Persian Gulf was the focus of the 1980–1988 Iran-Iraq War, in which each side attacked the other's oil tankers...

 region, Athel Formation in Oman

Oman

Oman , officially called the Sultanate of Oman , is an Arab state in southwest Asia on the southeast coast of the Arabian Peninsula. It is bordered by the United Arab Emirates to the northwest, Saudi Arabia to the west, and Yemen to the southwest. The coast is formed by the Arabian Sea on the...

, Bazhenov Formation and Achimov Formation in West Siberia, and Chicontepec Formation

Chicontepec Field

The Chicontepec Basin is a petroleum system in Mexico north-east of Mexico City, covering an area of around in the states of Veracruz, Puebla and Hidalgo. Several oil fields have been discovered in that area since 1926...

 in Mexico

Mexico

The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...

.