Propagation of nonlinear space-charge waves in an ion-beam–plasma system is investigated in a double-plasma device. The velocity of the beam is high enough to avoid ion–ion instability. The density ratio of the beam to the plasma is kept high ([les ]0.6), which makes the maximum amplitude of solitary waves large. The measured velocity and width of the compressional solitary waves of the fast and the slow beam mode are compared with predictions of the pseudopotential method in which the temperatures of beam and plasma ions are taken into consideration. Reasonable agreement is obtained between the experimental and theoretical results.