A calibration-free scanned wavelength modulation spectroscopy scheme requiring minimal laser characterization is presented. Species concentration and temperature are retrieved simultaneously from a single fit to a group of 2f/1f-WMS lineshapes acquired in one laser scan. The fitting algorithm includes a novel method to obtain the phase shift between laser intensity and wavelength modulation, and allows for a wavelength-dependent modulation amplitude. The scheme is demonstrated by detection of H(2)O concentration and temperature in atmospheric, premixed CH(4)/air flat flames using a sensor operating near 1.4 µm. The detection sensitivity for H(2)O at 2000 K was 4 × 10(-5) cm(-1) Hz(-1/2), and temperature was determined with a precision of 10 K and absolute accuracy of ~50 K. A parametric study of the dependence of H(2)O and temperature on distance to the burner and total fuel mass flow rate shows good agreement with 1D simulations.