The substitution rs and semi-experimental equilibrium reSE structures of the two conformers of 2ethylfuran were obtained using a combination of microwave spectroscopy and quantum chemistry. The microwave spectrum was recorded using a molecular jet Fourier-transform spectrometer operating in the frequency range of 2.0 GHz to 26.5 GHz. The spectra of all 13C and 18O isotopologues of both conformers could be measured in their natural abundances and the experimental gas-phase heavy atom structures were determined. All spectra were fitted using a semi-rigid rotor model including centrifugal distortion correction. The molecular geometries were compared with those of related molecules within the frame of the current literature. This work indicated that in some cases, the time required for recording survey scans of a Fourier-transform resonator setup can be reduced significantly with supports from adequate quantum chemical methods and spectral analysis skill.