A fluid analysis system is provided for analysis of a fluid flowing in a pipe or in a pipeline. The fluid analysis system comprises a pipe portion which, when the fluid analysis system is put to use, forms a part of the pipe or the pipeline through which the fluid flows. The pipe portion is provided with a fluid sample outlet for withdrawal of fluid samples from the fluid flowing through the pipe portion and a fluid sample return outlet for returning fluid samples to the pipe portion, where the fluid sample return outlet is arranged downstream of the fluid sample outlet. The fluid analysis system further comprises a fluid analyser which is provided in fluid communication with the fluid sample outlet and the fluid sample return outlet, and a propeller unit which is provided with at least one upstream propeller and at least one downstream propeller. The propeller unit is mounted in the pipe portion in such a manner that the upstream propeller is located upstream of the fluid sample outlet thereby enabling the upstream propeller to mix the fluid in the pipeline before fluid samples are withdrawn through the fluid sample outlet, and in such a manner that the downstream propeller is located downstream of the fluid sample outlet and upstream of the fluid sample return outlet.