The thermal cracking of oleic acid, a model fatty acid, in the temperature range of 390-450 degrees C was studied in the presence and absence of water. The effect of water on conversion yield and product distribution was determined. Analysis of the pyrolysis product by gas chromatography and mass spectrometry revealed the presence of expected compounds such as alkanes, alkenes, cyclic hydrocarbons, aromatics, and fatty acids in the liquid product. The results showed that distribution of the different classes of compounds was mainly dependent on the reaction temperature. In the absence of water, the products generated from pyrolysis of fatty acids at 430 and 450 degrees C yielded lower volumes of liquid product and higher amounts of aromatic compounds and solid residues than at 390 degrees C. However, these reactions still displayed high conversion and low fatty acid content. In the presence of water, an increase in liquid product yield was measured compared to pyrolysis conducted in the absence of water. However, the presence of water resulted in a remarkable drop in conversion (from 91.2 +/- 1.0% to 74.2 +/- 0.4%) at 390 degrees C. At 430 degrees C, the conversion did not change significantly in the presence of 5% water. At 450 degrees C, the conversion decreased slightly from 99.7 +/- 0.1 to 98.1 +/- 1.1 and to 98.2 +/- 0.8 in the presence of 5 and 10% water, respectively. Despite the lower conversion at 450 degrees C, the reduction in absolute amount was very small and thus the conversion rate was still close to 100%. At 450 degrees C, a decrease in solid residue yield and aromatics was also observed in the presence of water, while cyclic compounds increased at both 430 and 450 degrees C. The plausible underlying mechanisms have been discussed in this work.