This paper describes efficient data structures, namely the Indexed P-tree, Block P-tree, and Indexed-Block Ptree (or IP-tree, BP-tree, and IBP-tree, respectively, for short), for maintaining future events in a general purpose discrete event simulation system, and studies the performance of their event set algorithms under the event horizon principle. For comparison reasons, some well-known event set algorithms have been selected and studied, that is, the Dynamic-heap and the P-tree algorithms. To gain insight into the performance of the proposed event set algorithms and allow comparisons with the other selected algorithms, they are tested under a wide variety of conditions in an experimental way. The time needed for the execution of the Hold operation is taken as the measure for estimating the average time complexity of the algorithms.The experimental results show that the BP-tree algorithm and the IBP-tree algorithm behave very well with the event set of all the sizes and their performance is almost independent of the stochastic distributions.