Oil prices fell back below $100 a barrel in Thursday’s risk-off market action, dragging down exchange traded funds that invest in energy stocks.

These sector ETFs have benefited from the recent spike in oil prices, but performance among the funds can vary due to differences in the various tracking indexes.

In a research note, Isabelle Sender, S&P Capital IQ editor, compares two large-cap energy sector ETFs: the market-cap weighted SPDR Energy Select Sector Fund (NYSEArca: XLE) and the equal-weighted Rydex S&P Equal Weight Energy ETF (NYSEArca: RYE). [Oil ETFs Soar as Crude Tops $102 a Barrel]

“Underlying holdings’ weightings should be considered when deciding among energy ETFs,” Sender said.

The equal-weighted methodology allows small-cap holdings to exert greater influence on the overall movement of the fund while diminishing the influence of large-cap stocks. The market-cap weighted methodology allows the big and established firms to exert more influence the overall direction of a fund. [Oil and Gas Exploration, Production ETF Leads Rally with 50% Advance]

The majority of S&P’s analysts’ favorable rankings are for companies with $5 billion or more in market-cap. S&P Capital IQ Equity Analyst Stewart Glickman notes that large-cap energy stocks provide income generation, which makes up a large percentage of total return over the long-term, and relatively low volatility.

The equal-weight RYE has a 12-month yield of 0.58% while the market-cap weighted XLE has a 12-month yield of 1.55%, according to Morningstar.