The S.91 was a single-seat earlier single-bay biplane that resembled pursuit aircraft produced by André Herbermont except for its wing profile.

Despite the French government having lost interest in the general concept, the company opted to continue work for a time, promoting the S.91 to various prospective foreign operators.

The S.91 was a single-seat single-bay biplane developed towards the end of the 1920s by Blériot in order to meet the requirements of a French government program that sought a light fighter aircraft, which was referred to as "Jockey".

[3] In the vicinity of the cockpit, the lower wings featured a sight cut away in order to improve the pilot’s downward visibility, which was claimed to be quite good.

[4] Cooling was achieved using a Lamblin water-based radiators that was mounted on struts and positioned forward of the landing gear.

[4] It incorporated a hinged axle; each half-axle, which was relatively elevated in respect to the axis of the disk wheel, was likewise a box spar with a streamlined housing.

[4] The tail skid, which consisted of a spring with steel leaves, was hinged to the is sternpost of the fuselage and was attached at its upper end to a removable shock absorber.

During the flight testing of this initial aircraft, the company announced that it had attained a maximum speed of 270 km (168 miles) per hour while at an altitude of 4Q00 m (13,123 ft.).

[2] Furthermore, the prototype was claimed to be both highly manoeuvrable and relatively easy to operate as a result of its compact dimensions, favourable centring and the selected wing profile.

André Herbemont would use his experience with the S.91 prototypes in order to develop the S.510, another biplane fighter which would go into production and would be later used by the French Air Force.