The critical micelle concentrations of octylbetaine and N-octylbetaine were determined by three independent techniques; surface tension, density and light-scattering measurements. The values obtained were 0.097, 0.125, 0.120 mole/l for octylbetaine and 0.250, 0.250, 0.217 mole/l for N-octylbetaine. The micellar weights of these surfactants were estimated from the light-scattering data. These were 7.04×103for the former and 5.10×103for the latte