Crude oil prices drifted marginally lower in early Monday trading after Iran said it was preparing to put more of its petroleum products on the global market.

Crude oil prices suffered one of the worst days of the year Friday after Saudi officials said they'd agree to trim production provided other major market players followed suit. Russia has said it would back a freeze on production alongside members of the Organization of Petroleum Exporting Countries, though Iran said it would participate only after it gained a stronger market position.

Oil prices are lower in part because the market remains tilted toward the supply side. Adding to the pressure, the National Iranian Oil Co. said Monday it authorized sales of crude oil to Royal Dutch Shell now that the company has settled its debt obligations.

Crude oil prices fell further into negative territory in early Monday trading. Brent crude oil was down 0.7 percent to $38.39 per barrel. West Texas Intermediate, the U.S. benchmark price for crude oil, lost 0.2 percent to $36.73 per barrel.

Shell said the legal obstacles to settling its debt with Iran were lifted in March, though the company at the time said that was not necessarily indicative of an imminent market move.

During the weekend, Iranian Oil Minister Bijan Zangeneh confirmed Iran would continue producing and exporting more oil until it reaches the position it held before global economic sanctions went into full force in the early part of the decade.

Iran secured some relief from sanctions in January when it was confirmed it was meeting the terms of a multilateral nuclear agreement brokered last year.

Last week's declines were strengthened by a report from oil services company Baker Hughes showing the number of rigs in the United States fell to their lowest level in more than 60 years for their 15th straight week of declines. Weekend pressure emerged when leaked transcripts from the International Monetary Fund revealed lingering concerns about Greek debt, which cast a shadow over global economic health last year.