Imperial Oil Ltd. IMO -0.56 % on Friday posted a 90% drop in its second-quarter profit, hurt by a large charge for a tax-rate increase in Alberta, slumping global oil prices and in the absence of a year-earlier gain on the sale of an asset. The Calgary, Alberta, integrated energy company, the Canadian subsidiary of Exxon Mobil Corp. XOM -4.58 % , did get a boost from stronger production levels in the quarter, helped in part by the early startup of an oil-sands expansion project in northern Alberta. Overall production rose nearly 20% to 344,000 barrels of oil equivalent a day, which the company said was its highest quarterly production level in nearly eight years. In June, Imperial Oil announced that production from the Kearl oil-sands expansion project had started earlier than scheduled. The 9 billion Canadian dollar ($6.9 billion) project is expected to add 110,000 barrels a day […]