We present a systematic search for new classes of refrigerants that would possess low values of global warming potential (GWP), along with low- to moderate flammability and suitable thermodynamic characteristics. We have developed new methods for estimating, solely from the molecular structure, the radiative efficiency (RE, a measure of radiative climate forcing) and atmospheric lifetime; the combination of RE and lifetime yields an estimate of the GWP. We also developed an estimate of the lower flammability limit (LFL) based on the enthalpy of formation. These estimation techniques, along with a previously developed technique for estimating critical temperature (T-c), are applied to a library of over 56 000 candidate molecules. We select fluids with GWP < 200; 300 K < T-c < 550 K; and LFL > 0.1 kg.m(-3). Filters for toxicity and chemical stability based on functional groups are also applied to arrive at 1234 candidates for further study. The candidates that would be suitable for use in present types of refrigeration equipment (those having critical temperatures less than 400 K) are dominated by halogenated alkenes; additional chemical classes, including halogenated ethers and cyclic compounds, are identified among fluids with higher critical temperatures.