Pyrolysis and hydropyrolysis experiments at different temperatures, heating rates and pressures have been conducted on a sample of sunflower pressed bagasse to investigate the effect of particle size, sweep gas velocity, and hydrogen pressure on the product yields and characteristics. In contrast to coal and oil shales, char and oil yields from sunflower pressed bagasse were found to be largely independent of particle size and sweep gas velocity in a Heinze retort with the oil yield of approximate to 40% w/w being the same as that from a well-swept fixed-bed reactor in which a much smaller sample size was used. The use of high hydrogen pressure (> 50 bar) increased the oil yields by up to approximate to 10% w/w but these increases are much greater when expressed on a carbon basis due to the reduced oxygen contents of the oils. Even at low pressure, it has been estimated that approximate to 40% of the carbon aromatized during pyrolysis.