Methods and systems for forming water-in-oil emulsions are described. For example, an apparatus is described which includes: a first compartment containing a plurality of particles dispersed in an aqueous phase a second compartment containing an oil phase a porous layer separating the first and second compartments and a device for applying pressure to the first compartment. A method is described which includes: moving an oil phase relative to a surface of a porous layer while simultaneously forcing an aqueous composition comprising particles through the porous layer and into the flowing dispersion medium thereby forming droplets of the aqueous composition containing particles dispersed in the oil phase. The aqueous composition can include one or more nucleic acid templates and reagents for amplifying the nucleic acids such as PCR reagents. A porous partition is described comprising a first and second major surfaces and at least two straight through pores comprising a cross sectional shape selected from a polygon, an oval, an oblong, a dumbbell, a bowtie and irregular shapes thereof. Aqueous droplets containing an oligonucleotide attached to a particle and reagents can be used as a microreactor for nucleic acid amplification.Linvention concerne des procédés et des systèmes pour former des émulsions eau dans huile. Par exemple, un appareil décrit comprend : un premier compartiment contenant une pluralité de particules dispersées dans une phase aqueuse un second compartiment contenant une phase huileuse une couche poreuse séparant les premier et second compartiments et un dispositif pour appliquer une pression au premier compartiment. Le procédé décrit comprend : le déplacement dune phase huileuse par rapport à une surface dune couche poreuse en forçant de manière simultanée une composition aqueuse comportant des particules à travers la couche poreuse et dans le milieu de dispersion sécoulant, formant ainsi des gouttelettes de la composition aqueuse, contenant des part
