Why Indian petrol prices are high despite lower crude prices?

Three years after deregulation, petrol prices still seem to be in the control of the government. Last week, this paper pointed out that the fall in prices of petrol and diesel is less than that of the Indian crude basket. Over the last 18 months, while the Indian crude basket has fallen around 23% in dollar terms, local petrol prices have come down only by 4%. Why Indian petrol prices are so high despite lower crude prices?