Abstract Oil Palm (Elaeis guineensis) plantations cover more than 107,000 km2 in SE-Asia but there is little information on its photosynthetic characteristics. Photosynthesis in seedling, juvenile and adult Oil Palm (6 months, 1–2 y and >5 y old, respectively) were measured using blue-diode Pulse Amplitude Modulation Fluorometry (PAM). The Absorptance Factor of the leaves (Abt465nm) was measured using a Reflectance Absorptance Transmission (RAT) meter to calculate actual, rather than relative Electron Transport Rates (ETR). Midday measurements in juvenile and adult Oil Palm tree were: maximum quantum yield of Photosystem II (Ymax) in juveniles was about 0.63, Optimum irradiance (Eopt) was ≈300 μmol photon m−2 s−1. The maximum ETR (ETRmax) of juvenile plants was 24.06 ± 1.69 μmol e− m−2 s−1: based on 4e−/O2 this is equivalent to a maximum Photosynthetic Oxygen Evolution Rate (POERmax) of 89.21 ± 6.25 μmol O2 mg Chl a−1 h−1. Adult Oil Palm plants have a Ymax similar to juveniles but Eopt was ≈600 μmol photon m−2 s−1. The ETRmax of adult plants was 58.97 ± 2.07 μmol e− m−2 s−1: or POERmax = 305.3 ± 10.7 μmol O2 mg Chl a−1 h−1. Oil Palm is a classic sun plant with high photosynthetic rates at high irradiances. Photosynthetic efficiencies (α0) were high for C3 sun plants: α0 in adult plants (0.272 ± 0.018 e− photon−1) was higher than juvenile plants (0.204 ± 0.034 e− photon−1) expressed on a leaf surface area basis and on a Chl a basis (1.406 ± 0.093 vs. 0.757 ± 0.124 O2 photon−1 m2 g Chl a−1). In juvenile and adult plants Eopt, POERmax and α0 tend to maximize about midday. In seedlings, Eopt and POERmax are highest in the early morning but maximum α0 is at about midday. Oil Palms strategically optimize photosynthesis for high irradiances and manipulate their photosynthesis vs. irradiance characteristics during the course of daylight.