Th unseasonably warm winter temperatures and diminished demand for heating fuel have pushed natural gas inventories to record highs and pushed natgas-related exchange traded funds to all-time lows.

On Friday, the United States Natural Gas Fund (NYSEArca: UNG) fell 4.1% and United States 12 Month Natural Gas Fund (NYSEArca: UNL) dropped 2.9%. The three-times leveraged-long VelocityShares 3x Long Natural Gas ETN (NYSEArca: UGAZ) plunged 12.7%.

Nymex natural gas futures decreased 4.8% to $2.17 per million British thermal units Friday, hovering around a three-week low.

Meanwhile, ETF traders hedged against continued natural gas weakness with inverse ETFs. For instance, the VelocityShares Daily 3x Inverse Natural Gas ETN (NYSEArca: DGAZ) seeks to provide the daily inverse 3x, or -300%, performance of the NYMEX natural gas futures. The ProShares UltraShort Bloomberg Natural Gas (NYSEArca: KOLD) provides the daily inverse 2x, or -200%, performance. On Friday, DGAZ surged 11.9% and KOLD jumped 7.8%. [Are Inverse & Leveraged Natural Gas ETFs About To Skyrocket?]

The threat of an unusually mild December weather in some of the largest winter gas-consuming regions across the U.S. dragged on natural gas prices. The MDA Weather Services forecasts above normal temperatures across eastern states during the Thanksgiving Week with lingering warmth for the start of December, reports Naureen Malik for Bloomberg.

The lower demand for heating fuel has caused natural gas inventories to jump to an all-time high of 4 trillion cubic fee last week. Stockpiles may continue to build as production outpaces demand with mild weather delaying the start of the peak heating-demand season.

“The report yesterday showing the industry reached the 4 tcf level was certainly an important factor,” Teri Viswanath, director of commodities strategy at BNP Paribas, told Bloomberg. “The market is really looking at the possibility that warm weather will return in December, and the industry is going to be hard-pressed to take enough out of storage to rebalance the market in 2016.”

About half of U.S. homes use gas for heat, so a winter freeze has traditionally acted as the natural gas market’s chief driver of demand. However, an especially strong El Nino weather phenomenon has warmed the Pacific and added to forecasts for a mild winter across the Northern U.S.

“Near-term gas rally [is]unlikely given ample storage and the likelihood of incremental supply on the sidelines against a backdrop of El Nino warm-winter concerns,” energy-focused investment bank Tudor, Pickering, Holt & Co. said in a note, the Wall Street Journal reports.

United States Natural Gas Fund

For more information on the natgas market, visit our natural gas category.

Max Chen contributed to this article.