A chirp Fourier transform microwave spectrometer has been used to record the rotational spectra of two isomers of the hydrofluoroether C4F9OC2H5 (ethoxynonafluorobutane also known as HFE-7200) between 7.8 and 16.2 GHz. The target compound was spectroscopically examined as it participated in a supersonic expansion of argon. Four separate rotational spectra have been identified amongst the congested data. Spectroscopic parameters are presented for each species. The structures of all four species have been identified by exploring the multi-dimensional potential energy surfaces using quantum chemical calculations. (C) 2010 Elsevier B.V. All rights reserved.