The rotational spectrum of estragole has been investigated using a free-jet millimetre-wave spectrometer. Computational chemistry calculations at different levels of theory predict three possible conformers of estragole that are within 200 cm(-1) of each other. Analysis of the millimetre-wave spectrum clearly shows lines from two of the three possible conformers of estragole. The observed lines have been assigned to conformers I and III and their corresponding spectroscopic constants have been evaluated. Examination into why no lines from conformer II were observed was carried out by evaluating the potential energy surfaces linking the three conformers. (C) 2013 Elsevier B.V. All rights reserved.