A five-year chart for the United States Natural Gas Fund (NYSEArca: UNG) is not a pretty picture. Marred by multiple reverse splits and surging supplies thanks to the fracking boom, UNG has plunged 75% over the past five years.

This year has been far more kind to natural gas bulls. UNG is up nearly 26% year-to-date after one of the coldest winters in recent memory sent natural gas prices soaring. UNG and the iPath Dow Jones-UBS Natural Gas Total Return Sub-Index ETN (NYSEArca: GAZ) rank as the third- and fourth-best non-leveraged ETFs this year. [More Upside for Nat Gas ETFs]

More upside for UNG and GAZ could be on the way. “Inventories are 54 percent below the five-year average, the U.S. Energy Information Administration said last week,” Naureen S. Malik reports for Bloomberg. There is now a supply shortage of natural gas, one that will require more record production to stem the shortfall by October, according to Bloomberg.

That means natural gas could rally in the coming weeks if expectations of a warm summer increase. After the the coldest winter in 32 years forced Americans to burn through almost 3 trillion cubic feet of natural gas, market observers are looking toward the summer injection period and next winter. Stockpiles of up to 3 trillion cubic feet will be required to have the U.S. prepared for next winter. [Summer Shortfall Will Boost Nat Gas ETFs]

Data from the Commodities Futures Trading Commission indicate speculators have been upping their bullish wagers on natural gas futures contracts.