The incentives for re-engining the Lockheed P-3 ASW Patrol aircraft include reduced fuel consumption and therefore reduced operating costs (the P-3 currently accounts for 16 percent of the U.S. Navy's annual aviation fuel bill), increased mission effectiveness in terms of radius of action (ROA) and time on station (TOS) (when needed), increased sales potential/production life, increased service life, and reduced maintenance hours. For these reasons, Lockheed has for several years conducted both Navy-funded and in-house-funded engineering studies to identify the impact on performance and cost of re-engining the P-3 with either a derivative type or an all-new advanced turboprop (ATP) type engine. This paper discusses some of the results of these studies. In particular, the engines examined in these studies are compared from both a performance and installation design standpoint, with aircraft mission performance improvements identified. Program schedules and cost estimates are discussed, so that economic assessments/ trade-offs of the various options can be made. The paper also includes a discussion of current and far-term factors, which will affect the decision as to whether or not the P-3 aircraft is re-engined.