The largest exchange traded fund following natural gas futures was the top gainer in ETFs this week with a 9% rally, stirring hopes that the recovery in natural gas prices is real.

Natural Gas. The U.S. Energy Information Administration revealed a smaller-than-expected increase in natural gas inventories, stoking a rally in natural gas futures that have languished near a decade low. [Natural Gas ETF Clears 50-Day Average; First Time Since July 2011]

“All told, yesterday’s report strikes as bullish for the natty contract in the short to medium term,” Stephen Schork, editor of The Schork Report, said in an energy newsletter.

  • United States Natural Gas Fund (NYSEArca: UNG): up 9.3% over the last week.

Other top performers of the week include biotech and Treasuries.

Biotech. With ETFs, investors can gain a broad overview of the overall sector.

“I don’t want to be scattershot, covering every company I can. I really want to make sure I understand a field,” Rachel McMinn, the No. 1-ranked biotech analyst, said in a Wall Street Journal article.

McMinn is bullish on the industry’s 2012 prospects and believes that an influx of generalist investors will help boost the overall sector.

  • Market Vectors Biotech ETF (NYSEArca: BBH): up 4.2% over the last week.

Treasuries. With concerns of Greece exiting the euro hitting the market, investors found solace in U.S. Treasuries.