A concern about the declining supply of petroleum products has led to a renewed interest in evaluating plant species as potential alternate sources of energy. Five species of the Apocynaceae and three species of the Asclepiadaceae from the Western Ghats were evaluated as alternative sources of energy, oil, polyphenol, and phytochemicals. The highest protein content was observed in Caralluma attenuata with 6.6%. Plant samples of Aganosma cymosa yielded 10.3% oil. The highest polyphenol content was observed in Carissa carandas with 7.7%. Species of the Asclepiadaceae exhibited the highest quantity of hydrocarbon viz. Sarcostemma brevistigma (3.6%), C. attenuata (3.4%), and Tylophora asthmatica (2.7%). Carbohydrate content was high in S. brevistigma with 6.9%. A whole plant gross calorific value of 16.5 MJ kg(-1) for Nerium odorum (white flower variety) was the highest value observed. The highest gross calorific value observed in the oil fraction was from C. attenuata with 33.4 MJ kg-1. The hydrocarbon fraction of T. asthmatica exhibited the highest gross calorific value of 39.2 M Jkg(-1). The hydrocarbon fractions were further analyzed using NMR to determine the type of isoprene present. Fatty acid compositions of oil samples were also analyzed. All the species except N. odorum (white flower variety) contained higher quantities of saturated fatty acids than unsaturated fatty acids. (C) 2011 Elsevier Ltd. All rights reserved.