Solubilization of hydrocarbons in aqueous solutions of nonionic surfactants (mostly polyoxyethylene alkylphenyl ethers) has been investigated. The effects of the temperature, the nature and size of the solubilizates, and the oxyethylene chain length and the hydrocarbon chain length of the surfactants on the solubilization were elucidated. The effect of a small amount of added ionic surfactant (sodium dodecyl sulfate) on the solubilization has also been studied, and a comparison of the solubilizing power of ionic and nonionic surfactants has been made. The effects of the types of hydrocarbons (solubilizates) and the oxyethylene chain length of nonionic surface-active agents on the cloud points of nonionic agents in the presence of hydrocarbons were studied. These data are important for the selection of suitable nonionic surfactants for solubilization, emulsification, and detergent action.