In a process for making oil-containing, pressure rupturable capsules, a monomer which is polymerizable to a solid polymer is dissolved in an "oil" (i.e. a water-immiscible liquid) in which its polymer is insoluble, the oil solution is dispersed in a polar liquid, e.g. water, methanol, ethanol, glycerine, or ethylene glycol, and the monomer is caused to polymerize under the influence of a catalyst which may be introduced into the oil, into the monomer before dissolution thereof, into the monomer solution, into the polar liquid or into the dispersion, the polymer thus being formed on the surface of the dispersed oil droplets to form capsules.  Suitable monomeric materials are 10 : 1 and 4 : 1 mixtures of styrene and divinyl benzene, ethyl- and methylacrylates and methacrylates and vinyl acetate.  Specified catalysts are benzoyl peroxide, potassium persulphate, acetyl peroxide, di-tert-butyl peroxide, a , a -azo-di-iso-butyronitrile, hydrogen peroxide, calcium peroxide, zinc peroxide and sodium pyrophosphate peroxide.  The oils used may be of vegetable, mineral, animal or synthetic origin and may contain additional dissolved or dispersed materials.ALSO:Discrete, pressure - rupturable, micro- or macroscopic capsules containing an oil are produced by a process whereby at least one polymerizable monomer is dissolved in an oil, the oil solution is dispersed as droplets in a polar liquid and the monomer is polymerized on the surface of the droplets to produce an encapsulating shell of solid, oil-insoluble polymer. Polymerization may be induced by heat and a catalyst which may be introduced into the oil, into the monomer before its dissolution in the oil, into the oil solution of the monomer, into the polar liquid or into the oil dispersion therein.  Specific monomers mentioned are a mixture of styrene and divinyl benzene, ethyl and methyl acrylate and methacrylate, vinyl acetate.  The term "oil" refers to water-immiscible liquids, examples given being animal, vegetable, mineral and "artificial" oils, e.g. chlorinated diphenyl.  The polar liquid may be water (preferred), ethylene glycol, glycerine, ethanol, methanol and may contain emulsifying agents, e.g. gum arabic, sodium myristate, sorbitan monolaurate and monopalmitate, sodium alkyl sulphates.  Conventional catalysts which are oil or water soluble or insoluble may be used, e.g. benzoyl peroxide, potassium persulphate, a ,a -azo-di-isobutyronitrile, acetyl peroxide, hydrogen peroxide, calcium and zinc peroxides, sodium pyrophosphate peroxide, di-tert.-butyl peroxide. The invention also comprises capsules made as described above and having an additional external shell composed of a solid film-forming hydrophilic colloid material e.g. gelatine which is formed by coacervation of the colloid from a polar solution thereof and subsequently gelling and if desired hardening the colloid shell. Such capsules may be made by first preparing the dispersion of the monomer-containing oil and catalyst in the polar liquid adding a dispersion of the colloid material and adjusting the pH to cause coacervation of the colloid on to the droplets which by the time concervation is completed already have the polymer shell substantially formed.  Alternatively the formation of the polymer shell may be virtually completed before coacervation of the colloid is begun.  The oil within the capsules may have dissolved or dispersed therein dyes, pigments, inks, perfumes, fuels, adhesives, medicines, chemical reactants or the oil itself may be a marking fluid, fuel, perfume, chemical reactant or mixtures thereof.