This article describes the production and properties of gases produced by the pyrolyses of poly(ethylene terephthalate) (PET), polypropylene (PP), polyethylene (PE), poly(vinyl chloride) (PVC), and polystyrene (PS), and three of their mixtures at process temperatures of 500, 700, and 900 degrees C. The overall aim was to characterize all 24 gases in terms of their production and physical properties, and compare the data obtained to those of traditional fuels, namely natural gas (NG) and propane. In addition to experimental and analytical approaches for determining quantities and compositions of the pyrolysis products, various mathematical methods and their combinations were also used to determine product properties. The highest conversion of material into gas occurred during the pyrolysis of PP at 900 degrees C (66.88 wt% conversion into gaseous products). The pyrolyses of PE and PP at 500 degrees C were found to generate pyrolysis gases with the highest energy, with gross calorific values of 86.58 and 81.09 MJm(N)(-3) , respectively. The highest chemical energy yield was obtained by the pyrolysis of PP at 900 degrees C. Gases produced from PVC had a high thermal conductivity of about 104.83mWm(-1) K-1. The gas generated from PP at 500 degrees C exhibited a high specific heat of 2.94 kJm(N)(-3) K-1, and that obtained from PS at 500 degrees C had a very low kinematic viscosity (5.28 10(-6) m(2) s(-1)) and thermal diffusivity (7.90 10(-6) m(2) s(-1)). Even though numerous reports have dealt with pyrolysis gases, there is still not sufficient information about the specific physical properties of these gases. This article attempts to fill this gap and induce scientific interest in this field.