Processes and systems are provided for monitoring and blending a first stream and a second stream to produce a third stream of desired compositional characteristics. The processes and systems are found to be particularly useful for the blending of two or more hydrocarbon streams to economically produce a targeted hydrocarbon product stream meeting prescribed compositional specifications. Specifically, the processes and systems are found to be especially useful to blend a propane containing stream, having a vapor pressure lower than the vapor pressure of a targeted vapor pressure for a propane product, with an ethane containing stream. The blending processes and systems allow for production of an "on-spec" propane product stream while at the same time maximizing the value of the ethane stream. The processes and systems may incorporate continuous real-time analysis and flow control of the various streams to effectuate precise control the blending processes.