The fears recently expressed by the Energy Commission of Nigeria that the sun will slowly but certainly set on the country’s fossil-fuel-led economy coupled with the worldwide depletion of non- renewable energy sources and its attendant negative environmental impact have resulted in the need to consider alternative renewable fuel sources from the country’s abundant agricultural feedstock. One such crop is oil palm, from which palm kernel oil (PKO) is derived. Transesterification of PKO with ethanol to obtain PKO biodiesel was carried out using potassium hydroxide (KOH) catalyst. ASTM standard fuel tests performed on the PKO biodiesel gave promising results as alternative biodiesel fuel. Concentrations of catalysts have been widely reported as an important process parameter upon which biodiesel yield depends. Further in this work therefore, the effect of KOH concentration on PKO biodiesel yield is studied, with a view to identifying the catalyst concentration corresponding to optimal process yield. Three replicated transesterification experimental runs were carried out for each of the KOH concentrations 0.5 %, 0.75 %, 1.0 %, 1.25 %, 1.5 %, 1.75 % and 2.0 % (by mass of PKO) under identical typical transesterification reaction conditions of 60oC temperature, 120 minutes duration and 20 % ethanol (by mass of PKO). Results of the average PKO biodiesel yield for the respective catalyst concentrations are 90.5 %, 95.0 %, 95.8 %, 85.2 %, 73.3 %, 71.1 % and 71.3 %. The KOH concentration 1.0 % resulting in maximum PKO biodiesel yield (95.8 %) is therefore recommended as optimum, within the constraint of the typical transesterification process parameters used. These findings, agreeing well with earlier works, will find useful applications in the energy sector of the Nigerian economy.