By Eric Yep 
 

Crude-oil futures remained under pressure in Asian trade Tuesday, as investors monitor the progress of the Iranian nuclear talks in Vienna and a worsening Greek debt crisis.

On the New York Mercantile Exchange, light, sweet crude futures for delivery in August traded at $57.97 a barrel at 0258 GMT, down $0.36 in the Globex electronic session. August Brent crude on London's ICE Futures exchange fell $0.29 to $61.72 a barrel. Oil prices had lost around 2% in the previous trading session.

Greece looks set to default on its payment to the International Monetary Fund due Tuesday. Markets are also increasingly worried about the likelihood of Greece exiting the eurozone.

Meanwhile, Iran has dispatched two senior officials to the nuclear talks in Vienna in a last-minute push for a breakthrough, even as U.S. officials acknowledged the talks are likely to overshoot today's deadline.

There is significant concern in the oil market that Iran's output will increase quickly should an agreement be reached, with analysts forecasting a sharp increase in oil production by the end of 2015, eventually topping 4 million barrels a day.

"We believe the potential increase in Iran's output following any deal is likely to be far more limited than consensus expects," said Paul Horsnell, head of commodities research at Standard Chartered.

He said Iran hasn't produced 4 million barrels a day since August 2005, citing data from the U.S. Energy Information Administration (EIA), adding that the capabilities of Tehran's domestic oil industry have eroded due to Western sanctions in recent years.

"We estimate that Iran's sustainable capacity is now no higher than 3.2 million barrels a day, and we believe it will be a relatively long process to tackle the decline of output from the existing aging fields," Mr. Horsnell said.

Additionally, traders in Singapore said a large portion of Iranian oil in floating storage are condensates, a lighter form of crude oil used as feedstock in the petrochemical industry.

The American Petroleum Institute will publish its oil inventory report later Tuesday, followed by the U.S. EIA on Wednesday. Market estimates are for U.S. commercial crude stocks to fall by another 2 to 3 million barrels.

Nymex reformulated gasoline blendstock for July--the benchmark gasoline contract--fell 30 points to $2.0273 a gallon, while July diesel traded at $1.8390, 24 points higher.

ICE gasoil for July changed hands at $564.00 a metric ton, down $0.50 from Monday's settlement.

Write to Eric Yep at eric.yep@wsj.com

Laurence Norman and Jay Solomon contributed to this report