The present invention provides improved methods for purifying and/or removing oily particles, and/or contaminants suspended or dissolved in water. In particular the process relates to an additive composition that has the appropriate surfactant characteristics for effectively removing an oil phase from an oil/aqueous mixed phase via foam fractionation. According to the invention, a hydrophobically modified polymer that acts as an associative thickener is combined with surfactant in appropriate ratios to facilitate oil removal for water purification in any of a number of commercial, environmental and industrial applications.