The effects of extraction pressure, heating time, heating temperature, and extraction rime on the yield of mechanically expressed palm oil were studied. Extraction pressure ranged from 5 to 35 MN/m(2) heating time 10 to 40 min, heating temperature 80 degreesC to 140 degreesC and extraction time 2 to 30 min. Oil yield increased with extraction pressure up to 25 MN/m(2). Extraction pressures higher than 25 MN/m(2) did not result in any significant increase in yield. Yield increased with increasing heating time up to 20 min beyond which yield did not increase appreciably. As heating temperature increased, yield increased up to 100 degreesC heating temperature. Above 100 degreesC, the increase in yield was very small. Yield increased with extraction time and levelled off after 6-10 min extraction time depending on other parameters. Specific yield. Y-5 increased with extraction time, t nonlinearly yielding a logarithmic relation between Y-5 and t of the form Y-5 = 0.4015 e(0.1312t). (C) 2001 Elsevier Science Ltd. All rights reserved.