Millimeter- and submillimeter-wave spectra of regions such as the Orion molecular cloud show many rotational-torsional lines that are caused by the emission of complex organic molecules (COM). Previous laboratory investigations have been conducted for three isotopologues of ethyl cyanide up to 360GHz, and subsequently, several hundred lines of the three isotopologues have been detected in Orion IRc2 using the IRAM 30m radiotelescope. In this survey we present the analysis based on a Watson Hamiltonian for an asymmetric one-top rotor of the ^13^C-substituted ethyl cyanide ^13^CH_3_CH_2_CN, CH_3_^13^CH_2_CN and CH_3_CH_2_^13^CN in the frequency range 480-650GHz and 780-990GHz.The rotational spectra of the three species were measured with a submillimeter spectrometer (50-990GHz) using solid-state sources. A new set of spectroscopic parameters was determined from a least-squares fit procedure for each isotopologue. These parameters permit a new accurate prediction of rotational lines suitable for an astrophysical detection in the submillimeter wave range.