This paper is concerned with certain aspects of contention for main memory resources in a multiprogrammed computer system operating under demand paging. In the model presented, the number of page-frames of main memory allocated to a problem program varies in time. These changes in memory configuration are represented explicitly in the model, CPU requirements and page exception characteristics of program material being described statistically. Expressions for the distribution of the number of page-frames allocated to an executing program, the long run expected fraction of a program's execution time in a given number of page-frames, and the average execution interval of the multi-programmed load are obtained. It is pointed out heuristically and demonstrated numerically that an increase is obtainable in the average execution interval of the multiprogrammed load over that resulting from equal fixed partitioning of main memory. © 1972, ACM. All rights reserved.