Several chemical sensors have been developed using plastic optical fibers. Plastic optical fibers offer many advantages over glass fibers, such as high numerical aperture, low-cost, high flexibility, and ruggedness. The sensing segment is made of novel porous polymer fiber, combined with selective chemical indications systems. By careful selection of polymer systems and indicators, the chemical reagents can be covalently bonded to the porous plastic fiber. These sensors can be used to detect a variety of chemical species and to measure various chemical parameters, both in vapor and solution. They provide high sensitivity and stability. Sensor characteristics, including dynamic range, linearity, and response time, can be tailored to meet specific applications by altering the polymer composition and polymerization procedure. A low-cost, compact optoelectronic and data acquisition subsystem has been designed and constructed to interface with the sensor probe. This system employs two- wavelength, solid-state light sources, which allow the system to be calibrated on-line.