Profiles of velocity, species concentration (O-2, CO, and CO2), wall incident radiative heat flux and temperature are reported in the combustion space of a regenerative, side-port, 550 t/day, gas-fired flat-glass furnace. A region exists of fast-moving gases near the glass, with axial velocity components exceeding 20 m s(-1), and a large recirculation zone near the crown. Temperatures as high as 1985 K in the flame and as low as 1750 K in the recirculation zone are reported. A region of intense reaction is observed near the glass, with large concentration gradients and incomplete combustion even in the tail of the flame. Local incident radiant fluxes on the crown were nearly uniform spatially at a level of 680 kW m(-2). In the portnecks, flat inlet velocity profiles were measured with a magnitude of approximately 11 m s(-1). Significant variations were observed in the exhaust profiles of most measured variables. Large errors in exhaust mass balance suggest a complex, portnecks. A nominal preheat air temperature of 1420 K and a variation of exhaust temperatures between 1630 K and 1835 K were noted. O-2 concentrations as high as 8.4% were measured at the exit, suggesting a bypass of oxygen-rich flow around the flame. CO2 concentrations were the highest near the batch, where the glass reactions are the most intense.