AbstractInjecting soft, stable and size-controlled microgels to reduce water production is a new concept, introduced some years ago, we refer to as STARPOL process. Microgels specifically designed for water shutoff (WSO) treatments do not contain toxic products and can be produced to be fully self-repulsive. They adsorb onto rock pore surface by forming soft monolayers with a thickness equal to their size. This size can be adjusted as desired during the manufacturing process. As a consequence, water permeability can be reduced as desired. Microgel chemistry is chosen to be insensitive to pH and salinity variations.This paper reports laboratory results obtained with a new type of microgel expected to be available at industrial scale in a near future, under both powder and liquid form. The results include their characteristics in solution (size, intrinsic viscosity, mutual interactions and rheology), as well as their performances in porous media (model granular packs and Berea sandstones). These microgels were found to reduce water permeability strongly by forming thick adsorbed layers which are so soft that oil permeability is not affected. As expected from their crosslinked structure, their mechanical and thermal stability is excellent: shear rates as high as 1.5×104 s−1 or one month aging at 150°C do not reduce their viscosity. Another very significant advantage of microgels over gelling systems is that they can be quasi-ideally placed without need of zonal isolation when properly designed according to reservoir conditions: in this case, they penetrate almost exclusively into the highest permeability layers.