A hybrid approach to deriving tight execution-time bounds of program segments was proposed very recently. This approach symbiotically combines analytical and measurement-based methods to find a tight execution-time bound falling between the maximum measured execution time and an analytically derived loose bound. It also enables the estimation of the probability of the derived tight bound not being exceeded at run time.This paper provides a refined description of the hybrid approach and presents techniques for measuring the execution times of acyclic-path segments (APSs), which are possible execution sequences of instructions that contain no cycles and the basic units of analysis in the hybrid approach. In this paper, we also report the results of the hybrid approach in the derivation of tight execution-time bounds of three algorithms frequently used in the evaluation of WCET analysis techniques.