The law has been harshly attacked in Europe, but experts think only the French oil group Total among the big energy companies looks vulnerable to US sanctions.
"There are a few trapdoors built into this legislation," said analyst Adam Sieminski of NatWest Securities.
The law would slap US sanctions on foreign companies that make new investments of $40m or more a year in energy projects in Iran or Libya. President Clinton last month delayed implementing similar legislation against foreign companies doing business in Cuba.
The US says Iran and Libya support terrorism and prohibits its own companies from doing business with the two countries. It now wants foreign companies to toe the line, despite the objections of their governments.
But analysts pointed out that the US law covered future investments only and that sanctions were at President Clinton's discretion in many instances. Previously announced projects could be hit only if new investment was involved.
European governments denounced the law as unfairly imposing US rules on foreign companies while some European countries whose companies want to do business in Libya or Iran have threatened to retaliate.
Deutsche Morgan Grenfell analyst George Friesen said Total, with a refining and marketing business serving the central US, was most vulnerable to sanctions on its imports but was unlikely to be significantly hurt.
Repsol of Spain, Italy's ENI and PanCanadian Petroleum were other companies active in Libya or Iran, analysts said.
Asea Brown Boveri (ABB), the Swiss-Swedish engineering group, yesterday said it was seeking clarifications from US authorities on whether it could be affected by the US bill.