State-owned refiner Hindustan Petroleum Corp Ltd posted a 37.1 per cent fall in second-quarter profit on Thursday, dented by rising costs amid higher raw material and forex expenses.Net profit came in at Rs 1,092 crore ($148.62 million) in the quarter ended September 30, compared with Rs 1,735 crore a year earlier, HPCL said.Analysts had on an average expected a profit of Rs 1,511 crore, according to Refinitiv data.Income from operations surged nearly 35 per cent to Rs 73,065 crore.Average gross refining margin for the six months ended September 30 - the difference between the cost of crude oil processed and the price of refined products - dropped to $5.93 per barrel from $6.75 per barrel a year earlier.Shares in HPCL closed 2.2 per cent higher at Rs 229.15 apiece on the NSE, whose benchmark index Nifty finished flat after a choppy session, ahead of the earnings announcement by the company.($1 = Rs 73.4750)