Investors betting oil will rebound from the lowest prices in 5 1/2-years poured the most money in more than four years into funds that track crude. The four biggest oil exchange-traded products listed in the U.S. received a combined $1.23 billion in December, the most since May 2010, according to data compiled by Bloomberg. Another $109.9 million was added this month through Jan. 5. Investors are piling into oil ETFs even after West Texas Intermediate crude, the U.S. benchmark, tumbled the most since 2008 last year amid signs of rising supply and weak demand. Shares outstanding of the four funds surged to the highest since 2009. “Commodity investors can be contrarian investors,” said Matt Hougan, president of San Francisco-based research firm ETF.com. “There are a lot of true believers in the commodity space. A lot of people are attached to the idea that oil’s natural price should be $100, […]