Gel propulsion systems are of increasing interest due to their valuable energetic and safety considerations. In this paper, performance parameters of gelled UDMH/IRFNA bi-propellant were compared with performance parameters of its liquid bi-propellant. Fire tests were carried out with combustion chamber pressures of about 1 to 3 MPa and L* values of 89, 127 and 162 cm. The results showed that the suitable L* to obtain best performance for liquid UDMH/IRFNA combination at the mentioned conditions was 127 cm and for gelled UDMH/IRFNA bi-propellant was 162 cm, although the increase in performance with an increase of L* from 127 to 162 cm for the gel was very low.