Batches of 250 oil palm seeds from each progeny were heat-treated at a temperature of 39°C ± 1°C for 60, 80, 100 and 120 days, to break dormancy. Progenies with germination percentage of 50 % or more for all heat-treatment durations were planted out in the nursery using a Randomized Complete Block design, with heat-treatment durations as main plots and progenies as subplots. Seedling growth parameters measured included rate of leaf production, leaf area and relative leaf area growth rate