The specific surface area of amorphous Aerosil 200 and silica particles with 270 nm diameter prepared by the Stoeber method was investigated by a variety of experimental methods: nitrogen adsorption at 77 and 253 K; adsorption from ethanol/cyclohexane mixture; heats of wetting measurements; small-angle X-ray scattering (SAXS) experiments. The N-2 adsorption isotherms at 77 K were analyzed using the BET equation, the modified BET equations of Toth, and equations of the uniform interpretation method of Toth. For Aerosil 200, the values of the specific surface varied slightly depending on the applied method. For Stoeber silica, the results from nitrogen adsorption at 77 K ranged between 18 and 24 m(2)/g; these values were 20-30 times smaller than those derived from N2 adsorption at 253 K, binary liquid mixture adsorption, and heats of wetting or SAYS experiments (439-670 m(2)/g). The specific surface area of Stoeber silica estimated from nitrogen adsorption measurement at 77 K could not be applied to adsorption data from liquid medium; the other methods, however, provided reliable surface area and charge density values. According to the pore size distribution curves from thermogravimetry, two mean pore diameter values are distinguished (2 and 16 nm), but larger pores also exist in the structure of the Stoeber silica particles. According to the SAXS results Stoeber silica has a mass fractal structure (D-m = 1.73) on the length scale of 5-25 nm.