Bubble formation in agarose gels as a result of rapid decompression following saturation with either N2, CO2, or He has been studied. Bubble number was observed to vary predominantly as a function of decompression magnitude and was virtually independent of the particular gas used. The cavitation threshold (i.e., 1 bubble in 50% of trials) was found to fall between -3 and -4 psig ( approximately -0.25 atm) for all three gases. Modification of the ionic content of the agarose gel medium, either by lowering the pH or including polyvalent cations, had only slight effects, if any, on the number of bubbles produced by a given decompression. From these results, and the work of others briefly reviewed in the paper, it is concluded that the surfactant monolayer surrounding a gas cavitation nucleus is comprised almost exclusively of nonionic surface-active molecules.