The ability to detect and measure a variety of gases under certain environmental conditions has significant potential impact in many areas; from hazardous gas detection in the industrial domain to physical sciences in academia. Gas sensing has long received attention with microwave and infrared spectroscopy. With many molecular resonances occurring in the THz (T-ray) range leading to simple, unique spectral features, THz time-domain spectroscopy (TDS) promises to be a potential tool for gas detection. This paper presents a preliminary study on real-time gas recognition with THz-TDS. In particular, a simple method is proposed that involves extracting line positions from gas species without a reference pulse and classifying them by means of the minimum Euclidean distance using the Submillimeter, Millimeter, and Microwave Spectral Line Catalog.