Oscillatory flow reactors (OFRs) are a novel type of continuous reactor, consisting of tubes containing equally spaced orifice plate baffles. An oscillatory motion is superimposed upon the net flow of the process fluid, creating flow patterns conducive to efficient heat and mass transfer, whilst maintaining plug flow. Unlike conventional plug flow reactors, where a minimum Reynolds number must be maintained, the degree of mixing is independent of the net flow, allowing long residence times to be achieved in a reactor of greatly reduced length-to-diameter ratio. Many long residence time processes are currently performed in batch, as conventional designs of plug flow reactor prove to be impractical due to their high length-to-diameter ratios, which lead to problems such as high capital cost, large 'footprint', high pumping costs and, also control is difficult. The OFR allows these processes to be converted to continuous, thereby intensifying the process. The transesterification of various natural oils to form 'biodiesel' is a 'long' reaction, usually performed in batch. Conversion to continuous processing should improve the economics of the process, as the improved mixing should generate a better product (rendering the downstream separation processes easier), at lower residence time (reduction in reactor volume). These improvements can decrease the price of 'biodiesel', making it a more realistic competitor to 'petrodiesel'. This paper shows that it is feasible to perform this reaction in an OFR at a lower residence time. The reaction was performed in a pilot-scale plant, using rapeseed oil and methanol as the feedstocks, and NaOH as the catalyst. (C) 2003 Society of Chemical Industry.