Petrol price was cut by 91 paise a litre on Sunday, the seventh reduction since August, and diesel by 84 paise per litre, the third straight cut, as international oil rates continued to slump.Petrol and diesel price reduction will be effective midnight tonight, Indian Oil Corp, the nation’s largest fuel retailer, announced here.In Delhi, petrol price will cost Rs 63.33 a litre as compared to Rs 64.24 per litre previously while in Mumbai the reduction will be 96 paise to Rs 70.95 per litre.Diesel will cost Rs 52.51 a litre in Delhi from Monday as against Rs 53.35 currently while in Mumbai the price will be cut by 93 paise to Rs 60.11 per litre. Rates differ from state to state due to differential local sales tax or VAT rates.The prices of petrol and diesel were last revised downwards on November 1 by Rs 2.41 a litre and Rs 2.25 per litre respectively (including state levies at Delhi) on the back of declining international oil prices.”Since the last price changes, the international prices of both petrol and diesel have continued to be on a downtrend. The Rupee-USD exchange rate has however appreciated since the last price change. The combined impact of both these factors warrant a decrease in retail selling prices of both petrol and diesel,” IOC said in the statement.This is the seventh consecutive reduction in petrol prices since August and third in diesel in rates since October. Prior to today’s reduction, petrol price has been cumulatively cut by Rs 9.36 per litre since August.Diesel price was cut for the first time in more than five years on October 19 by Rs 3.37 a litre when the government decided to deregulate the fuel. This was followed by another reduction on November 1.”The movement of prices in international oil market and Rupee-Dollar exchange rate shall continue to be closely monitored and developing trends of the market will be reflected in future price changes,” the statement said. Rates would have been cut by Rs 1.50 on November 16 but the government took away the gains by way of an excise duty increase.Excise duty on normal or unbranded petrol was hiked from Rs 1.20 per litre to Rs 2.70 per litre and unbranded diesel from Rs 1.46 a litre to Rs 2.96. The same on branded petrol was raised from Rs 2.35 a litre to Rs 3.85 and on branded diesel from Rs 3.75 to Rs 5.25 per litre.While the fall in global rates and the resultant cuts in retail prices have led to loss of revenue to the exchequer, particularly of state governments, there wasn’t any loss to the central government on account of reduction in petrol and diesel prices as excise duty on the two fuel is fixed and not ad valorem. The increase in excise duty would give the government of Rs 13,000 crore additional revenue annually.State-owned fuel retailers Indian Oil Corp (IOC), Bharat Petroleum Corp (BPCL) and Hindustan Petroleum Corp (HPCL) follow the fortnightly review practice and change rates on 1st and 16th of every month.Oil firms revise rates of petrol, which was deregulated in June 2010, and diesel on 1st and 16th of every month based on average international oil price and rupee-US dollar exchange rate.