The present invention relates to an agent for dyeing and/or bleaching keratinous fibers, comprising: a water-in-oil emulsion (A) comprising one or more basifying agents, water, one or more surfactants having an HLB of less than 8, chosen from oxyalkylenated and/or glycerolated nonionic surfactants, and from 30 to 70% by weight, with respect to the total weight of the emulsion (A), of one or more oils not comprising a carboxylic acid functional group, and a second composition (B) comprising one or more oxidizing agents, the total amount of oil(s) not comprising a carboxylic acid functional group in the mixture of the emulsion (A) and of the composition (B) representing at least 20% by weight, with respect to the total weight of the mixture of these two compositions. The present invention also relates to a method for dyeing and/or bleaching keratinous fibers employing such an agent and to a kit comprising it.
