Ascent Resources LLC, one of the largest privately held U.S. natural gas producers, is preparing an initial public offering (IPO) it hopes will give it a market valuation of around $6 billion, according to people familiar with the matter. Depending on timing, it would be the first major stock market listing of a U.S. shale operator since Russia's invasion of Ukraine in February drove a spike in gas prices. The ensuing stock market volatility that prevented many companies from launching an IPO is now subsiding and energy prices remain elevated, making it a favorable environment for Ascent to consider pursuing a listing.