The United States Oil Fund (NYSEArca: USO) fell 2.3% Monday to another all-time low while West Texas Intermediate futures slid to the lowest levels in over five and a half years.

Yet oil’s downward spiral is not deterring investors from making value bets on equity-based energy sector exchange traded funds. Actually, investors are flocking to ETFs such as the Energy Select Sector SPDR (NYSEArca: XLE).

Even with oil prices down 20% this month, investors have allocated $3.16 billion to energy ETFs, or “almost four times the average for the year and more than the prior record in December 2007, when oil was trading near $91 a barrel,” reports Jim Polson for Bloomberg.

XLE, the largest equity-based energy ETF, has brought in $1.9 billion in new assets this month, a total surpassed by just two ETFs. That brings XLE’s fourth-quarter inflows north of $2.9 billion. Despite being the only one of the nine sector SPDR ETFs to trade lower this year, no sector ETF has added more new assets than XLE and just nine ETFs of any type have seen greater inflows. [Buying the Dip in Energy ETFs]

On a historical basis, XLE is the second-best of the nine sector SPDRs in the month of December, trailing only the Materials Select Sector SPDR (NYSEArca: XLB). Since 1999, the first full trading year for the sector SPDRs issued by State Street Global Advisors, XLE has posted an average December gain of 2.5%. XLE is up nearly 0.4% this month. [Sector ETF Ideas for December]