An oil-in-water emulsion comprises an emulsifier which is a non-gelled branched polymer (e.g. a branched vinyl polymer), wherein the ends of at least some of the chains of said polymer terminate in an alkyl chain of 5 carbon atoms or more, and wherein the oil-in-water emulsion takes the form of particles having a z-average diameter of no greater than about 1000 nm. This is useful in, for example, facilitating the carrying of hydrophobic materials within aqueous systems, to enhance oral drug delivery. The oil-in-water emulsion may be prepared by mixing an oil phase with an aqueous phase in the presence of an emulsifier, wherein said emulsifier is a non-gelled branched polymer, wherein the ends of at least some of the chains of said polymer terminate in an alkyl chain of 5 carbon atoms or more, and wherein the oil-in-water emulsion takes the form of particles having a z-average diameter of no greater than about 1000 nm. The oil phase may comprise a further solvent which is miscible with the oil, said solvent being allowed to evaporate to produce the final emulsion.