There are many environmental and process-control sensor applications where speed and reversibility are more important than selectivity. These might include monitoring the fate and transport of contaminants in laboratory columns and microcosms, measuring hydrocarbons in waste treatment streams, mapping the extent of a plume of a known contaminant, or monitoring solvent concentrations (e.g., acetone, dichloromethane, etc.) in a manufacturing process stream. In each case, there is prior knowledge of the type of contaminant and interferences, and in many cases the target molecule is at a relatively high concentration. For such applications, the sensor should be fast and reversible to allow real-time tracking of rapidly changing concentrations; however, it does not need to be very selective and might even respond to a wide variety of compounds. We are exploring new types of sensors for these applications. The sensors are based on reversible color changes that occur when solvatochromic (SV) dyes experience polarity changes. The optical sensors are made by immobilizing the SV dye in a polymer film that is coated on the end of a clad optical fiber or on the sides (i.e., evanescent region) of an unclad optical fiber. For the sensors described here interaction of a fluorescent SV dye with analyte vapors changes the amount of light absorbed by the dye and thus the fluorescence intensity that is measured with the optical fiber. Initial experiments have focused on fuel-related contaminants (e.g., xylene, benzene), and commercial solvents (e.g., acetone, dichloromethane--DCM). This paper will focus on the xylene and DCM results.