Volume rendering by ray casting is computationally expensive. For interactive volume visualization, rendering must be done in real time (30 frames/s). Since the typical size of a 3D dataset is 2563, parallel processing is imperative. In this paper, we present anO(logn) EREW algorithm for volume rendering. We useO(n 3) processors that can be optimized toO(log3 n) time withO(n 3/log3 n) processors. We have implemented our algorithm on a MasPar MP-1. The implementation results show that a frame of size 2563 is generated in 11 s by 4096 processors. This time can be further reduced by the use of large number of processors.