A memorandum of understanding was signed late last month by OMV, the Austrian energy group, and similar recent accords were inked with Anglo-Dutch Royal Dutch Shell and Repsol, of Spain.

These companies are trying to keep their options open until the international diplomatic situation improves or Iran forces them to stop procrastinating, Financial Times reported.

Frank Harris, analyst at Wood Mackenzie, the consulting group, said, “Access to gas around the world is getting tougher and the big players cannot afford to ignore Iran. They need to retain the option to participate in Iran because the political winds may change, which is why we are seeing the non-binding deals.“

Last month, Gholamhossein Nozari, managing director of Iran’s state-owned oil company and deputy energy minister, said he had given Total, the French energy group, four more months to decide whether to invest some $2bn-$4bn in the South Pars natural gas project. The earlier deadline was March 31.

Iran gave Total the extension because the country needs an experienced company to get its liquefied natural gas (LNG) industry off the ground. Total argued it had to consider the fact that the project’s costs had doubled because of a worldwide industry shortage of labor and equipment.

Lukoil, Russia’s second biggest oil company, is in the early stages of investment in Iran and still had 12-18 months before having to decide on any major expenditure.

In the past three years, Chinese, Indian and Malaysian companies agreed to invest more than $90bn to purchase Iranian gas, develop oil and gas fields and build pipelines, LNG terminals and other energy infrastructure, according to Kenneth Katzman, a Middle East expert at the Congressional Research Service.

China National Offshore Oil Company is negotiating a $16bn dollar deal to develop Iran’s North Pars gas field.