LONDON (AFP) -- Oil prices dropped on Wednesday before the release of U.S. energy inventory data and after calls by Iran for talks to resolve its nuclear standoff.

In London, Brent North Sea crude for October delivery slid 51 cents to 72.73 dollars per barrel in electronic deals.

New York's main contract, light sweet crude for delivery in October, lost 55 cents to 72.55 dollars per barrel in pit trading.

The September contract expired Tuesday priced at 72.63 dollars.

The weekly update on U.S. oil reserves by the Department of Energy later Wednesday will be watched closely by traders as the American driving season winds down.

"We are expecting lower stocks this week but with the end of the driving season coming, the market may be pricing in a slower demand," said Mark Pervan, a commodities analyst with Daiwa Securities in Melbourne.

The U.S. summer driving season sees Americans taking to the roads on vacation, leading to higher demand for motor fuel.

Traders' focus at the start of this week, meanwhile, has fallen on Iran, the world's fourth-biggest producer of crude oil.

Iran on Tuesday delivered its response to a deal aimed at ending the long-running nuclear dispute but did not say if it had met the demands of the international community.

Iran pumps about 4.0 million barrels of oil per day of which around 2.7 million barrels are exported, and analysts argue that vital supplies could be affected if sanctions are imposed on the Islamic republic.

"Diplomats are currently examining the response and so we wait to hear their verdicts, but it still seems likely that sanctions will be imposed and that will mean there is still a possibility that Iran could halt oil exports," Sucden analyst Michael Davies said Wednesday.

Iran's nuclear negotiator Ali Larijani delivered the written response to representatives of the five permanent Security Council members plus Germany, which drew up the package of incentives for Iran to renounce uranium enrichment and reprocessing activities.

U.S. officials said they would study Tehran's Tuesday response carefully, but added that they were ready to move ahead quickly in seeking UN enforcement action if Iran did not suspend sensitive nuclear fuel cycle work as demanded by the UN Security Council.

The European Union said the document required careful analysis.

Iran says its nuclear program is purely for peaceful power generation but Washington suspects it is a cover for an attempt to produce a bomb.