One aspect that separates real planning problems from toy problems is that solutions to real problems must be not only correct but also efficient and high quality. In this paper, we will describe the Least Commitment Operator Selection (LCOS) strategy which enables planners to construct globally optimal plans. The LCOS was developed from studies of human expert planners solving complex problems. Producing efficient, high quality plans is difficult because in most complex domains, some operators may share cost or between them. It is necessary to take a global view of the plan in order to make globally optimal operator choices resulting in a high quality plan. The LCOS strategy structures search in such a way that global considerations can be utilized, and and more efficient plans can be produced.