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In general, a measurement of fluid force per unit area (measured in units such as pounds per square in.) subtracted from a higher measurement of fluid force per unit area. This comparison could be made between pressures outside and inside a pipe, a pressure vessel, before and after an obstruction in a flow path, or simply between two points along any fluid path, such as two points along the inside of a pipe or across a packer.

The change in force per unit area measured across various downhole tools such as measurements-while-drilling (MWD) tools, downhole turbines and mud motors.

The difference between two pressure measurements. For production wells, the differential pressure is the difference between average reservoir pressure and bottomhole pressure, and for injection wells, it is the difference between injection pressure and average reservoir pressure.

A condition whereby the drillstring cannot be moved (rotated or reciprocated) along the axis of the wellbore. Differential sticking typically occurs when high-contact forces caused by low reservoir pressures, high wellbore pressures, or both, are exerted over a sufficiently large area of the drillstring. Differential sticking is, for most drilling organizations, the greatest drilling problem worldwide in terms of time and financial cost. It is important to note that the sticking force is a product of the differential pressure between the wellbore and the reservoir and the area that the differential pressure is acting upon. This means that a relatively low differential pressure (delta p) applied over a large working area can be just as effective in sticking the pipe as can a high differential pressure applied over a small area.