In machine learning there is considerable interest in techniques which improve planning ability. Initial investigations have identified a wide variety of techniques to address this issue. Progress has been hampered by the utility problem, a basic tradeoff between the benefit of learned knowledge and the cost to locate and apply relevant knowledge. In this paper we describe the COMPOSER system. COMPOSER embodies a probabilistic solution to the utility problem. It is implemented in the PRODIGY architecture. We compare COMPOSER to four other approaches which appear in the literature: (1) PRODIGY/EBL's Utility Analysis; (2) STATIC's Nonrecursive Hypothesis; (3) DYNAMIC: A Composite System; and (4) PALO's Chernoff Bounds. (Contains 24 references.) (Author/ALF)