New Delhi, July 9 -- Global oil prices are off their war-time highs, even if the US-Iran peace pipe coughs up fumes of anger now and then-crude futures rose mid-week on a White House threat to walk away.

Back home, however, petroleum has been simmering for a different reason. In India, motorists complain of reduced mileage and increased wear-and-tear observed in their vehicles due to the use of petrol blended with 20% ethanol as staple fuel, as mandated by the government.

E20 refills took effect last year, but protests grew shrill once a plan was announced to bump ethanol up to 25%. The Centre has assured vehicle users that such a step would be taken only after tests are done.

Those tests are unlikely to defy science. Ethanol has a low...