When police bring the traffic to an abrupt halt in Raipur, capital of the remote Indian state of Chhattisgarh, drivers know what to expect next. Soon, flashing red lights atop speeding government vehicles come into view. Raman Singh, Chhattisgarh's chief minister, is passing through.

Government motorcades are a common sight in Indian capitals. But what is different about this one is that all of Chhattisgarh's official vehicles, including the chief minister's Tata Safari jeep, are run on oil from the wrinkled black nut of a shrub-like tree called jatropha.