NEW DELHI: The government today hiked excise duty on petrol and diesel by Rs 2 per litre each to take away gains coming by way of global oil prices dipping to six-year lows.Retail pump rates will remain unchanged as the increase in excise duty neutralises the cut in petrol and diesel prices warranted from crude oil price slumping to about $46 per barrel.This is the fourth increase in excise duty on the two fuels since November and cumulatively customers have been denied the benefit of Rs 7.75 per litre reduction in petrol and Rs 6.50 a litre cut in diesel rates that was warranted due to the slump. Finance Ministry notification said excise duty on unbranded petrol is being hiked to Rs 8.95 per litre and that on unbranded diesel to Rs 7.96 per litre.The four excise duty hikes will result in about Rs 20,000 crore in additional revenue this fiscal and will help the government meet its fiscal deficit target of 4.1 per cent of the GDP.Earlier in the day, Petroleum Minister Dharmendra Pradhan responded to criticism of oil firms not cutting despite near 4 per cent fall in global rates since January 1 saying, the pricing was "not in our hands" as the two fuels have been deregulated."What oil companies feel appropriate they will do," he said.Alongside Pradhan, B Ashok, Chairman of Indian Oil Corp, the nation's largest fuel retailer, justified the decision not to revise rates saying oil firms were saddled with huge inventory which need to be compensated.The crude oil that is being processed currently in refineries is one that was bought about 6-8 weeks back when rates were higher than present prices. By the time, it is processed and marketed its market value would have come down, resulting in inventory losses, totalling about Rs 12,000 crore."There is huge drop in crude prices which is having a tremendous impact on our inventories, its a cash loss. We are paying much higher price for the crude and today we are processing the crude at a much lower price and passing it. We are taking our decision based on that and we think we have been doing the right thing," Ashok said.The Finance Ministry notification said the excise duty hike will be effective from midnight tonight.The government had last raised excise duty on petrol and diesel by Rs 2 per litre each from January 2. Prior to that, the tax was hiked by Rs 1.50 a litre each from November 12 and Rs 2.25 per litre on petrol and Re 1 on diesel from December 2.Global crude oil prices have fallen almost 50 per cent since June 2014, the most since the 2008 financial crisis, as supplies swelled.In April-September, IOC, Bharat Petroleum Corp Ltd (BPCL) and Hindustan Petroleum Corp Ltd (HPCL) had an inventory loss of Rs 5,300 crore which has risen by "two to three times" since then, an official said.Petrol and diesel prices were last cut on December 16 by Rs 2 per litre each. This was the eighth straight reduction in petrol prices since August, and fourth in diesel since October.Petrol in Delhi today costs Rs 61.33 a litre, the lowest in 44 months. Diesel costs Rs 50.51 a litre, the lowest since July 2013.Since August, petrol price have been cut by Rs 12.27 per litre on a cumulative basis while diesel rates in four downward revisions have been slashed by a total of Rs 8.46 a litre. Crude oil price in June was at $115 per barrel.