Process for fast pyrolysis of biomass organic particles, characterized in that it makes use of a fast pyrolysis reactor with entrained flow of biomass organic particles, comprising: - a tubular reaction chamber in which the pyrolysis reaction of particles takes place, including an upper part and a lower part opposite the upper part, - device for injection of particles in the upper part of the reaction chamber, to form a flow of particles dropping by gravity in the reaction chamber, - an evacuation duct for products originating from the pyrolysis reaction and present in the reaction chamber, including gases and pyrolyzed particles designed particularly to form pyrolytic oil, pyrolytic coke also called "char", and incondensable gases, - a counter current hot neutral gases injection duct 6 in the lower part of the reaction chamber making it possible to form a counter current flow FC of hot neutral gases coming into contact with the flow of particles 2 dropping by gravity, so as to generate the fast pyrolysis reaction of the particles 2, said process comprising the step for counter current injection of hot neutral gases into the reaction chamber of the reactor in the direction opposite to the direction of particles dropping by gravity, on which the fast pyrolysis reaction will take place, the temperature of the hot neutral gases being between 500 and 600°C, and the diameter of the particles being between 200 μm and 1 mm, the injection device of particles including a reservoir of particles, containing particles and located outside the reaction chamber, a tubular injector of particles located in the upper part of the reaction chamber, and means of transporting particles originating from the reservoir to the tubular injector, the reactor comprising means of injecting an entrainment gas in the upper part of the reaction chamber, in the tubular injector of the injection device, said process comprising the step to inject an entrainment gas into the reaction chamber of the reactor, to improve injection of particles into the reaction chamber. - a tubular reaction chamber in which the pyrolysis reaction of particles takes place, including an upper part and a lower part opposite the upper part, - device for injection of particles in the upper part of the reaction chamber, to form a flow of particles dropping by gravity in the reaction chamber, - an evacuation duct for products originating from the pyrolysis reaction and present in the reaction chamber, including gases and pyrolyzed particles designed particularly to form pyrolytic oil, pyrolytic coke also called "char", and incondensable gases, - a counter current hot neutral gases injection duct 6 in the lower part of the reaction chamber making it possible to form a counter current flow FC of hot neutral gases coming into contact with the flow of particles 2 dropping by gravity, so as to generate the fast pyrolysis reaction of the particles 2, said process comprising the step for counter current injection of hot neutral gases into the reaction chamber of the reactor in the direction opposite to the direction of particles dropping by gravity, on which the fast pyrolysis reaction will take place, the temperature of the hot neutral gases being between 500 and 600°C, and the diameter of the particles being between 200 μm and 1 mm,