Warren Buffett’s Berkshire Hathaway (NYSE: BRK-A) acquired 40 million shares of Dow component Exxon Mobil (NYSE: XOM), the largest U.S. company, during the third quarter, according to filing with the Securities and Exchange Commission.

Based on Thursday’s closing prices, Berkshire’s Exxon stake was worth $3.74 billion. Berkshire hasn’t held any ExxonMobil since the end of 2011, when it sold a relatively small stake of 421,800 shares, according to CNBC.

Since Buffett is one of the most widely followed investors in history, news of Berkshire’s new investment in Exxon could be meaningful in the near-term for ETFs with large weights to the stock. The Energy Select Sector SPDR (NYSEArca: XLE), the largest energy sector ETF, allocated 15.8% of its weight to Exxon as of Wednesday. [Sector SPDRs Still Going Strong]

The Vanguard Energy ETF (NYSEArca: VDE) held a 21.2% Exxon weight at the end of October while the iShares U.S. Energy ETF (NYSEArca: IYE) allocates 22.5% of its weight to the stock. The new Fidelity MSCI Energy Index Fund (NYSEArca: FENY) has an Exxon weight of nearly 22%. [Fidelity Launches 10 Sector ETFs]

Berkshire trimmed its stake in ConocoPhillips (NYSE: COP), the largest independent U.S. oil and gas producer.