The adsorption of an odour compound common in drinking water, 2-methylisoborneol (MIB), was studied on two activated carbons in the presence of 13 well-characterised natural organic matter (NOM) solutions. It was found that, although the carbons and the NOM solutions had a wide range of characteristics, the major competitive mechanism was the same in all cases. The low molecular weight NOM compounds were the most competitive, participating in a direct competition with the MIB molecule for adsorption sites. Equivalent background concentration (EBC) calculations indicated a relatively low concentration of directly competing compounds in the NOM. Some evidence of pore restriction was also seen, with microporous carbons most affected by low molecular weight NOM, and mesoporous carbons impacted by the higher molecular weight compounds.