In situ measurements of the interaction force between surfaces hydrophobized by physical adsorption of surfactants in solutions and the direct observation of the morphology of adsorbed surfactants were conducted for trimethylammonium chlorides with alkyl chains of six different lengths, using a tapping mode AFM. It is found that (1) a strong and long-range attractive force with a discontinuous step is observed, when surfactants with a sufficiently long alkyl chain are employed, (2) the bubblelike domains and the corresponding force curves are obtained directly, (3) the long-range interaction never appears when a completely air-free solution of surfactants is prepared, and (4) the usual degassing method of solutions does not necessarily guarantee that surfactant solutions are degassed when they contain stabilized bubbles. Hence, it is concluded that the long-range attraction is attributable to the gas bridge formed between surfaces due to the coalescence of stabilized microscopic bubbles on the surfaces wh...