The reflection coefficient for plane waves incident obliquely on a medium in which the velocity decreases exponentially is computed approximately using the WKB method and compared with a computation from the rigorous solution. The approximate reflection coefficient1/[16(ω/g)2 cos6θ+1]where ω is the angular frequency,gis the velocity gradient at the start of the exponential decrease, and θ the angle of incidence is within 0.05 percent of the rigorous value for ω/g⩾ 5 at normal incidence and within 5 percent of the rigorous value for ω/g⩾ 20 for angles of incidence up to about 45°.