Some of the world's largest companies have dropped financial support and membership of free-market think tank the Institute of Public Affairs amid concern at its vociferous campaign against action on climate change.

Petroleum giants ExxonMobil and Shell and large miners are among the multinationals that have confirmed leaving the Liberal-linked IPA, led by party member John Roskam, who this year was compared to Jesus Christ with his disciples by Opposition Leader Tony Abbott.

John Roskam of the Institute of Public Affairs. Credit:Ken Irwin

Despite the loss of this support The Sunday Age can reveal the IPA is now Australia's wealthiest private think tank after a surge in donations and fund-raising from individuals that helped it double its revenue in just four years.

It has a burgeoning media presence with an eightfold increase in TV, radio and newspaper mentions in the past decade.