The HELIOS experiment has measured inclusive p⊥ spectra of negative particles in the rapidity region 1.0<y<1.9. The general shape of the p⊥ spectra in p +W, O+W and S+W is similar, but cannot be described by a single exponential. Compared to p+p collisions, an excess is observed for low and high p⊥. This effect increases with the projectile mass. Except for very low E⊥, the average transverse momentum <p⊥> is found to be approximately constant up to the highest accessible values of E⊥.