This study concerned the conversion of black liquor organic components during heat treatment in the liquid phase. The liquor was treated for 45 minutes at 350-degrees-C after a sodium hydroxide charge of 15-45% of the mass of black liquor dry solids. A hydrophobic, lignin-derived oil product (about 40% of initial organics) was formed, in addition to volatile products (about 35% of initial organics) and fragments remaining in the aqueous phase. Detailed GLC analysis of the low-molecular-weight aqueous phase components indicated the presence of various aliphatic carboxylic acids (5-20% of initial organics). These acids were primarily degradation products of the original acid fraction of the feed black liquor. The influence of conversion conditions on the composition of the acid fraction is discussed.