Momentum at the Iranian nuclear negotiating table put additional pressure on crude oil prices for a second day, with Brent down more than 2 percent Tuesday.

Foreign diplomats gathered Tuesday in Switzerland to join U.S. Secretary of State John Kerry and Iranian delegates working to hammer out a nuclear deal in the waning hours of a self-imposed deadline. The State Department said there's a modest chance of success, though Russian Foreign Minister Sergei Lavrov said the prospects were "good" that some sort of deal would be arranged.

Iran in November 2013 secured relief from some economic sanctions and allowed limited crude oil exports in exchange for limiting its nuclear research activity. A breakthrough at the negotiating table in Switzerland would open an Iranian spigot on a market already favoring the supply side.

Brent crude oil for May delivery was down more than 2 percent to below $55 per barrel as markets waited for final word on the status of the nuclear talks.

For the United States, now rivaling Saudi Arabia in terms of crude oil production, output is progressing at record levels. Crude oil production increased 1.2 million barrels per day last year to 8.7 million bpd. In terms of percentage, that's the largest increase in 75 years.

West Texas Intermediate, the U.S. benchmark, fell 1.9 percent from Monday's close to trade near $47.76 per barrel in early Tuesday trading.