A downhole tool for perforating a well and obtaining fluid samples therefrom, comprises a retrievable packer (20), perforating guns (24) and a sampler (22) disposed between the packer and guns which is adapted for entrapping a fluid sample without flowing well fluids into the tool string. An operating piston is slidably disposed in a cylinder above the packer and is used to actuate a sampler valve in the sampler. A seal ensures that all portions of a sampling chamber in the sampler are disposed below the packer. The operating piston is actuated in response to a pressure differential between a well annulus above the packer and an internal pressure in the tool. The sampler includes a plurality of sampler modules disposed in the sampling chamber. Each of the sampler modules includes a valve which automatically closes after a predetermined volume of fluid fills a sampler module chamber defined in the sampler module.