Biofuels analyzers and Hydrocarbon Sensors. FuelCX(TM) is a vehicle-mounted or process-integrated sensor for measuring the biofuel content, as well as indicating the type and quality of biofuel (such as feedstock, degree of refining, or biodegradation) used in mixture of biofuel and petroleum fuel, such as biodiesel and petroleum diesel. FuelCX continuously operates in the entire range from zero to 100% biofuels content, and any value in between. The sensor illuminates fuel mixture with visible, near-UV or UV photons to excite fluorescence emissions, acquires the spectrum of fluorescence as raw data, and applies an algorithm analyzing the Stokes shift and other attributes on the spectrum to calculate the biofuel concentration, feedstock, and various quality indicators. FuelCX can be integrated in, or added to the fuel systems of vehicles, watercraft, or aircraft, and/or installed in the fuel lines in vehicles and fuel dispensing stations. It can also be used as a side stream device for large diameter fuel lines, such as in industrial process pipes or vessels. Connectivity options include wired options such as CANbus, MODbus, SPI, or custom protocols, as well as wireless options including LoRa, Bluetooth, and WiFi.