This big gorilla is set to jump into oil futures market

Nikodash | iStock/Getty Images Plus

The United States Oil Fund, ticker "USO," is set to jump into the futures market this week, rolling a huge share of the outstanding U.S. oil futures contracts from May into June.

Traders are keeping a keen eye on the exchange-traded security, set to roll out of its more than 60,000 West Texas Intermediate futures contracts for May delivery into June, as volatility continues to rock the crude market.

The ETF, a more than $3 billion fund and the industry heavyweight, reports its monthly activities ahead of time on its website and says it plans to roll over its holdings in U.S. oil futures between Tuesday and Friday.

The oil ETFs hold about a third of the combined open interest in May WTI futures, traded on the Nymex and ICE, according to ETF Securities.

For investors in the fund and oil market, they may see little impact on the surface. But since oil is in contango—meaning forward futures contracts are more costly than current contracts—the fund could certainly pay up for and influence the price of June futures contracts.

Read MoreOil may strengthen, then hit new lows - Gartman

"It will be closely watched because obviously, it's a long-only fund and the roll should exaggerate the contango in the front of the market," said John Kilduff of Again Capital. Under its mandate, USO each month sells its entire front-month futures position and purchases the next month.

As for the ETF investors, Eric Mustin, vice president of ETF trading solutions at WallachBeth Capital, says the monthly roll can affect the ETF price somewhat and when the market is in contango, it can cost.

Read MoreOil spike may take a little longer - Hall

Mustin said the spread beween May and June futures on Monday was just about 2.5 percent. "Over the course of the week, if you're a long-term holder, you have to give up a small premium or have some percent of erosion just to maintain your exposure," as the fund buys the more expensive contracts, he said.

Read MoreIran nuke deal - these industries could get a boost

"I think it's a well-managed fund, and that's the kind of exposure investors ask for when they buy into the fund," Mustin added. He noted that USO has grown by $1.7 billion just this year.

As for the oil market, the actions of USO are less likely to show up with recent volatility sending oil sky high some days and sharply lower others. On Monday, WTI futures jumped 6.1 percent in their largest one-day gain since early February on speculation of rising demand and on the weaker dollar. Oil was down slightly Tuesday.

Oil ETFs were holding between 170 to 180 million barrels equivalent of WTI futures for May, according to ETF Securities. USO controls 64,000 contracts of that—or 64 million barrels equivalent of WTI futures for May, the firm said.

Read MoreWhen oil will hit bottom

"There's maybe a market impact on the relative spread between the first two months because they're selling May and buying June. But other than that, on the flat price, no. It's well in the market what days the rolls are so some people might try to trade ahead of it," said Andrew Lipow, president of Lipow Oil Associates.

Kilduff also said the activity could show up as a slight widening of the spread between the front month and June. "It's relative," he said. "If it's an overall down day in the complex, it would be down but maybe not that much."