It is shown that theoretically, in most cases of interest, the acoustic radiation pressure exerted by plane traveling waves on small rigid and liquid spheres is determined by viscous and heat effects whereas the classical King [Proc. R. Soc. London, Ser. A147, 212–240 (1934)] and Yosioka and Kawasima [Acustica5, 167–173 (1955)] results are only negligible corrections.