The generations of dielectric barrier discharge (DBD) in high-pressure nitrogen and carbon dioxide environments up to supercritical conditions with or without flow fields were performed. From the second positive system of nitrogen, the rotational temperature of N-2 was estimated to be approximately 400 K under a supercritical N-2 condition (4 MPa and 313 K). On the other hand, from emission spectra of DBD in a high-pressure CO2 environment (1-8 MPa), C-2 and O spectra were remarkable in intensity instead of CO, CO+, CO2 and CO2+ spectra that were remarkable at atmospheric pressure. Furthermore, porous carbon film synthesis by DBD under a supercritical CO2 condition (7.5 MPa and 305 K) was also identified by scanning electron microscopy observation. (c) 2005 Elsevier B.V. All rights reserved.