Crude oil prices are on track for their largest annual gain since the financial crisis, but oil exchange traded fund investors should keep in mind that ETFs track the futures market, not the spot price.

Oil prices are rebounding after Saudi Arabia and its allies in the Organization of Petroleum Exporting Countries, along with other non-OPEC producers, pledged to cut output to end the global glut that depressed crude prices for two years.

After bottoming out earlier this year, West Texas Intermediate crude oil futures are now trading around $53.7 per barrel and Brent crude futures were hovering around $56.7 per barrel.

U.S. crude is up about 45% year-to-date while Brent is up about 50%, marking their best year since 2009, reports Timothy Puko for the Wall Street Journal.

However, the United States Oil Fund (NYSEArca: USO), which tracks West Texas Intermediate crude oil futures, is only up 6.6% year-to-date and the United States Brent Oil Fund (NYSEArca: BNO), which tracks Brent crude oil futures, gained 28.2% so far this year.

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