The effects of the velocity gradient and nonadiabaticity on the extinc
tion of premixed counterflow low-pressure flames were studied using sa
turated laser-induced fluorescence of OH radicals. The temperature and
OH concentration were determined at a stagnation point for different
opposed flow velocities in nonadiabatic and near-adiabatic methane-oxy
gen-nitrogen flames in the range of equivalence ratio 0.6-1.2. The tem
perature and OH concentration profiles were measured in twin flames fa
r from and close to extinction. Temperatures at the stagnation point v
ary with heat losses and velocity gradient, while OH concentrations de
pend mainly on velocity gradient. Spatial gradients of temperature or
OH concentration profiles in twin flames are insensitive to velocity g
radient and heat losses. The implication of these results for the corr
ectness of probe sampling and mass-spectrometric analysis in low-press
ure flat flames is discussed.