In descriptive sensory techniques, reference materials are used to establish a common vocabulary for various aromas and flavors. A reference standard can be any chemical or natural material that adequately represents the particular characteristic described. This paper evaluates the utility of various reference materials that have been proposed as odor standards. The odor reference library used included odors commonly attributable to microbiological and industrial sources. The results of utilizing reference standards demonstrated that some materials were very good; that is, they yielded a distinctive odor that transcended cultural and language differences, as well as different levels of experience. Other aromas required several standards to distinguish among subtle but important differences, e.g., geosmin and 2-methylisoborneol to differentiate earthy/musty odors. These standards also included natural materials prepared in various states to reference different types of common odors in water - for example, grass clippings (in water) that had been freshly cut to represent a grassy odor, or had been held for a week to represent a septic odor, as well as dried grass for a hay odor. Other reference materials yielded bimodal distributions in which, primarily, two groups centered around different descriptors; these kinds of materials would not make good reference standards.