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Traditionally, electrodynamic shakers have been used to test nonlinear systems using sinusoidalexcitation. However random excitation is desirable due to its lower testing times. Inboth cases, shakers affect system dynamics when used to test relatively light structures byintroducing additional impedance. On the other hand, pneumatic excitation, a new techniquedeveloped at UC-SDRL [1] used for linear system identification, is used here to testnonlinear systems. This thesis focuses on testing a rig with a flexible beam with a knowncubic nonlinearity using both a traditional electrodynamic shaker as well as the pneumaticexcitation method. The results of these two methods are compared with each other.The property of nonlinear systems showing the presence of uncorrelated response at harmonicsof the natural frequency is used in this thesis to investigate asymmetry in the system.Bilinearity present in the system due to asymmetry which was hard to detect from shakertest was clearly evident in pneumatic excitation test. The dips in the coherence functionpresent due to harmonics of nonlinear response is differentiated from leakage errors usinga nonlinearity detection algorithm developed at UC-SDRL. The presence of bilinearity isfurther confirmed by static loading tests in both directions as well as dynamic testing inthe loaded conguration. The conclusions of the comparative study are presented and advantagesof using pneumatic excitation over traditional shaker excitation are stated in the end.