Ocean thermal energy conversion (OTEC) is a solution for environmental and climate change issues in the tropics. The OTEC potential in Malaysia using ocean conditions and bathymetry data has been previously studied and demonstrated. Following this, it is vital to perform a basic performance analysis of a 10 MW Rankine Cycle OTEC plant using the Malaysian ocean conditions. In this paper, the results of heat and mass balance will be reported for a 10 MW Rankine cycle OTEC plant which uses heat exchangers of plate-type and anhydrous ammonia as its working fluid. The value of a minimum objective function (γ) is derived by total heat surface area (AT) divided by the net power (PN). γ decreases when the inlet temperature difference (inlet temperature of warm seawater (TWSWI)—inlet temperature of cold seawater (TCSWI)) increases. PN is clarified to be approximately 70–80% of the PG (gross power) using Malaysian ocean conditions.