The carbon aromaticity of five Australian coals and their flash pyrolysis products was measured by 13C solidstate n.m.r. In all cases, the products contained the same or more aromatic carbon than the coals. The amount of aliphatic carbon converted to aromatic carbon varied from ≈ 0–32%. The variability in the extent of aliphatic carbon aromatization may be due to the different amounts of hydroaromatic or long-chain aliphatic carbon in these coals. For some flash pyrolysis tars, direct measurements of aromaticity by crosspolarization, solid-state 13C n.m.r. are erroneous. This is due to mobile CH 2 material in the tar, which has a T CH longer than the T 1 ϱ H of the rest of the tar, so that accurate measurements of aromaticity must be made by Bloch decay methods.