* Four barrels of light crude spilled in derailment * Second oil spill for railway in a week * Shares down 2.4 pct April 3 (Reuters) - Canadian Pacific Railway Ltd suffered its second oil spill in a week on Wednesday, but said just four barrels of light crude leaked from tanker cars in a morning derailment in a remote area of northern Ontario. CP, Canada's No. 2 railway, said 20 cars in a 128-car mixed-freight train destined for Montreal derailed near White River, about 700 kilometers (400 miles) northeast of Toronto. It said two tankers temporarily leaked crude following the incident. CP said the oil has been contained and there were no injuries. The spill comes a week after 14 cars on a 94-car CP train derailed near Parkers Prairie, Minnesota, spilling close to 15,000 gallons (360 barrels) of Canadian oil bound for U.S. refiners and raising questions about the safety of shipping crude by rail. That was first major spill since a boom in North American oil production prompted a huge rise in crude-by-rail transport as oil output began to outgrow the existing pipeline network. The railway and Canada's Transportation Safety Board are investigating the cause of the White River derailment. The company could not yet say when the line will reopen. CP shares were down C$3.11 at C$123.23 late on Wednesday afternoon on the Toronto Stock Exchange. The White River area is best known as the birthplace of Winnie, the London Zoo bear that inspired the A.A. Milne's children's classic Winnie the Pooh.