We present the results of a quantitative spectroscopic analysis of DR1, an oxygen sequence Wolf-Rayet (WO) star in the low-metallicity galaxy IC 1613. The high-excitation oxygen emission of WO stars is usually attributed to the surfacing of the element during the late stages of helium burning. Alternatively, it has been suggested that the oxygen emission is purely a temperature effect. To investigate the nature of WO stars, we have modelled the spectrum of DR1 using the radiative transfer code CMFGEN, aiming to constrain the stellar and wind parameters. Our results indicate that the oxygen abundance is not enhanced compared to values found for early-type carbon sequence Wolf-Rayet (WC) stars. The properties of DR1 instead suggest that WO stars are the high-temperature extention of the WC class, and not neccesarily in a more advanced evolutionary state.