When investors think about ESG (short for environmental, social and corporate governance) standards, usually they don’t think of an oil and gas exchange traded fund. In fact, legacy fossil fuel-focused companies often get vilified as directly opposed to the environmental standards that form a key part of ESG.

Still, the iShares US Oil & Gas Exploration &Production ETF (BATS:IEO) which is stuffed with big oil names such as ConocoPhillips (COP), Marathon Petroleum (MRO), Valero Energy (VLO), Devon Energy (DVN), Phillips 66 (PSX) and Hess Corp (HES), somehow finds itself at the top of multiple ESG ratings leaderboards.

While the U.S. does not have a universal ESG rating system, many independent firms generate ratings for investors. MSCI is one firm that provides this service, giving a comprehensive system that rates ETFs from a CCC to AAA. (AAA represents the best ESG score, while CCC designates the lowest rating.)

According to MSCI data, IEO is a AAA-rated ESG ETF that falls in the upper 95th percentile among globally listed ETFs.

MSCI outlines that 77% of IEO’s holdings received an A, AA, or AAA rating while only 1% of its positions received a CCC. See a breakdown below:

MSCI is not the only firm to provide IEO with an ESG stamp of approval. ETF database, a leading exchange traded fund information provider, gave IEO a 9.47 ESG score out of 10.

With its exemplary rating, IEO actually ended up with a better score than many popular clean energy funds, such as the First Trust Global Wind Energy ETF (FAN), iShares Global Clean Energy ETF (NASDAQ:ICLN), Global X Wind Energy ETF (WNDY), First Trust NASDAQ Clean Edge Green Energy Index Fund (QCLN), and the Invesco Solar ETF (NYSEARCA:TAN).

Furthermore, IEO is not the only oil and gas ETF to get an ESG stamp of approval. According to ETF database, Energy Select Sector SPDR Fund (NYSEARCA:XLE), Strive U.S. Energy ETF (DRLL) and iShares U.S. Energy ETF (IYE) all received a higher rating than 9.

So how do these oil and gas names filter high on ESG leaderboards? The answer is that it’s not all about the environmental aspect — although that’s the focus it often gets in popular media.

Many of the major oil and gas companies score high on the corporate governance part of the equation, with high marks for the social aspects as well. Diversified boards, social safeguards, and movement away from other screens like controversial weapons and tobacco help overcome some environmental concerns.

For more on the investing prospects for IEO, see why Seeking Alpha contributor Juan de la Hoz called the investment vehicle an ETF “for aggressive oil bulls.”