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.
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"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.
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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.
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"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.
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"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."