PERT (Program Evaluation and Review Technique) estimates each task duration from three points — optimistic, most likely, and pessimistic — to produce a weighted expected duration and a measure of uncertainty. This makes it well-suited to research and development projects with unfamiliar tasks.
PERT is often used alongside the Critical Path Method; CPM finds the longest path while PERT quantifies the probability of meeting a given completion date. Monte Carlo simulation is a modern extension.