The United States Oil Fund (NYSEArca: USO) is up 6.6% this week and 4.5% this month. Earlier this week, Royal Dutch Shell (NYSE: RDS-A), Europe’s largest oil company, said it is acquiring rival BG Group for $70.2 billion in the oil industry’s largest acquisition in a decade.

Those headlines and more are boosting the fortunes of some oil stocks and the corresponding exchange traded funds, but investors looking to play a recovery in the energy sector might do well to stick with basic, familiar equity-based energy ETFs.

That includes the Vanguard Energy ETF (NYSEArca: VDE). After a recent fee-reduction, something Vanguard has become famous for, VDE has an annual expense ratio of 0.12%, tying it with the Fidelity MSCI Energy Index ETF (NYSEArca: FENY) for the title of least expensive energy ETF. [New Fee Cuts From Vanguard]

Like rival cap-weighted energy ETFs, VDE is heavily allocated to Dow components Exxon Mobil (NYSE: XOM) and Chevron (NYSE: CVX). The two largest U.S. oil companies combined for 33.4% of the ETF’s weight at the end of February, according to Vanguard data.

“While these two firms represent a large chunk of assets, they operate in a diverse set of businesses across the energy complex. Their operations range from exploration and production all the way down to distribution. This helps temper the supermajors’ sensitivity to energy prices but does not eliminate it entirely,” according to a new research note from Morningstar.

The energy sector  has been an attractive play from a so-called mean-reservation perspective – the idea that prices and returns eventually move back towards the mean or average. Now that the energy sector has experienced a large pullback, traders are anticipating the sector will at the very least revert back to its historical average. [Returning to Energy ETFs]