The SEC will likely approve the 1 billion extra units for the U.S. Natural Gas Fund ( UNG), paving the way for more investors to gain exposure to the natural gas market. The last few weeks have been a whirlwind for UNG traders as the popular ETF has essentially operated as a closed-end fund pending the release of the new shares.As creation of UNG ground to a halt, both traders and regulators were faced with the reality of the fund's influence on the commodity it was designed to track. UNG was forced to stop selling new shares July 7 because it reached the limit of shares it was approved by regulators to create. UNG assets have gone from about $400 million in January 2008 to almost $4 billion. The creation and redemption process helps keep ETFs in line with NAV, and UNG has been disjointed from its underlying value since regulators stepped in. The fund has traded at both a premium and a discount as traders wait for the new shares to be issued. While the additional units should help to put UNG back in line, the recent hiccough in share creation raises important questions about the fund and the ETF industry as a whole. UNG and its sister fund U.S. Oil Fund ( USO) essentially allow investors to trade commodities as if they were stocks. The question among issuers has not been "should" but rather "could" when it comes to introducing increasingly complex ETFs, and the roll strategies that underlie these funds are far more complex than many investors would like -- or want -- to wrap their minds around.