Car companies General Motors India, Hyundai and Mahindra-Renault will soon bring out model variants that will run on either LPG or CNG. GM’s Chevrolet Optra already has a CNG variant available in Delhi, Mumbai and Vadodara. Mahindra-Renault, too, is selling the CNG version of the Logan for the taxi market in Mumbai. CNG and LPG are not only ‘greener’ fuels compared to petrol and diesel, but are also cheaper. However, consumers will have to shell out between Rs.35,000 and Rs.50,000 more for the gas variants.