Canadian Natural Resources has agreed to buy its rival Rio Alto Exploration for about C$2.4 billion (US$1.54 billion) in cash or stock and assumed debt, merging companies with stakes held by the oil financier Murray Edwards. Rio Alto stockholders will get C$18.10 a share or 0.35 of a Canadian Natural share, 13 percent above Rio Alto's closing price at the end of last week, the companies said in a statement. Canadian Natural will assume C$972 million in debt. Rio Alto holders also will get shares of a new company owning assets in South America. The purchase will boost Canadian Natural's output of natural gas by forty five percent, making it the second largest Canadian producer. Edwards had 2.32 million Canadian Natural shares as of March 31 and was the biggest individual holder of Rio Alto with 701,100 shares. Rio Alto stock had tumbled after estimates of gas in its Canadian fields were slashed by a third. The offer is “the best Rio Alto can do under the circumstances,” said Kevin Nyysola, a fund manager for Investors Group, Canada's largest mutual fund.