Abstract: A flow restriction is placed in the pipeline through which the fluid to be sampled flows to provide a pressure drop that is proportional to the rate of flow of the fluid in the line. A sample bottle is connected to the line through a sample conduit that also contains a flow restriction to cause a pressure drop in the fluid flowing to the sample bottle. A variable flow restriction in the sample line downstream of the first flow restriction is adjusted to maintain the pressure drop across the flow restriction in the sample line proportional to the pressure drop across the flow restriction in the pipeline so that fluid flows into the sample bottle at a rate that is proportional to the rate of flow of fluid in the pipeline.