New Delhi, Oct. 29 -- Carbon tax concessions granted to global oil giants may undermine incentives to shift to cleaner energy, environmentalists fear.

So conservation groups in Singapore are seeking more transparency over what discounts the city-state of 6 million giving polluters for taxes on their climate-changing emissions. Singapore is the only Southeast Asian country to have imposed a carbon tax so far. Most of the European Union, California, South Korea and Japan also do so.

Indonesia, Malaysia and Thailand are preparing to implement similar taxes next year and Vietnam and Brunei are considering the idea. The groups are pressing the Singaporean government to disclose more information about "allowances" Singapore's National Climate...