It has been calculated that some fish can achieve a propulsive efficiency greater than 90%.

The physics of propulsive efficiency may be stated succinctly as follows.

Propulsive efficiency determines how much energy vehicles generate from a unit of fuel.

In addition, propulsive efficiency is greatly dependent on air density and airspeed.

From these principles it can be shown that the propulsive efficiency for a rocket moving at speed with an exhaust velocity is:

To each flight velocity, there corresponds a particular value of propulsive efficiency and specific fuel consumption .

This phenomenon is termed propulsive efficiency ().

Due to jet engines being propulsive efficiency, Concorde burned two tonnes of fuel taxiing to the runway.

The actual overall system energy efficiency in use is determined by the propulsive efficiency, which depends on vehicle speed and exhaust speed.

Mathematically, it is represented as where is the cycle efficiency and is the propulsive efficiency.

The original 'low-bypass turbofan' engines were designed to improve propulsive efficiency by reducing the exhaust velocity to a value closer to that of the aircraft.

In addition to propulsive efficiency, another factor is cycle efficiency; essentially a jet engine is typically a form of heat engine.

Rocket engines have a slightly different propulsive efficiency () than airbreathing jet engines as the lack of intake air changes the form of the equation.

At the lower end of I the overall efficiency drops, because the ionization takes up a larger percentage energy, and at the high end propulsive efficiency is reduced.

Controllable pitch propellers (CPP) for marine propulsion systems have been designed to give the highest propulsive efficiency over a broad range of speeds and load conditions.

In cruise, the combination of distributed boundary-layer ingestion and wake filling increase propulsive efficiency, while distributed vectored thrust provides substantial improvements in pressure drag.

In practice, a higher energy than this is needed to be expended due to losses such as airdrag, propulsive efficiency, cycle efficiency of engines that are employed and gravity drag.

There is the possibility of a tripropellant combination, which takes advantage of the ability of substances with smaller atoms to attain a greater exhaust velocity, and hence propulsive efficiency, at a given temperature.

Stalin's decision that the Project 69 ships would use three shafts increased the shaft loading and reduced propulsive efficiency, although it did shorten the length of the armored citadel and thus overall displacement.

Tank bottom weights provide a much shorter lever arm, so need to be a much larger proportion of the total ballast, but do not interfere with propulsive efficiency the way ankle weights do.

The reliable Solo 2325 engine is mated to a small diameter 'paddle' propeller that sacrifices a small amount of propulsive efficiency in exchange for much smaller drag if the engine fails to start.

Assuming a typical propulsive efficiency of 86% (for the optimal airspeed and air density conditions for the given propeller design), maximum overall propulsive efficiency is estimated as:

Bell Helicopter's assessment resulted in validations of the MTR-SD vertical lift capacity, engine power required and power available, cruise thrust and propulsive efficiency, aircraft weight, and airplane mode cruise lift.

For all airbreathing jet engines the propulsive efficiency (essentially energy efficiency) is highest when the engine emits an exhaust jet at a speed that is the same as, or nearly the same as, the vehicle velocity.

In aircraft and rocket design, overall propulsive efficiency is the efficiency, in percent, with which the energy contained in a vehicle's propellant is converted into useful energy, to replace losses due to air drag, gravity, and acceleration.