Three major oil companies preparing to drill off the shores of Guyana, where a string of discoveries have sparked a rush for crude, are being challenged by a group of citizens who say their dash for oil is illegal.

Lawyers acting for the Guyanese campaigners are to lodge the latest challenge in a court in Guyana this week. They are funding the battle against oil giants Exxon Mobil, Hess Corporation and Nexen, a subsidiary of Chinese national oil, through the crowdfunding site CrowdJustice.

Offshore drilling off the coast of Guyana is seen as one of the most sought-after prospects in the world for oil companies. Analysts predict offshore drilling could provide 350,000 to 400,000 barrels a day by 2026, while Exxon has predicted 500,000 barrels a day.

But concerned citizens of the small South American country, which has never been an oil producer, are challenging the oil giants.

Melinda Janki, one of the lawyers representing the Guyanese campaigners, said the granting of licences to drill by the government was illegal. Under Guyanese law, a licence to drill can only be granted if an environmental permit has been obtained by the company involved.

“It is very simple. If you want to extract oil in Guyana you need an environmental permit in order to get a petroleum production licence,” she said. “Only one of the three companies involved has an environmental permit. We are seeking an order to quash the decision by the minister to issue the licence because, we are saying, he acted illegally.”

Janki lodged an appeal earlier this month after the first attempt to quash the granting of the licences was rejected by a judge.

Ramon Gaskin of A Fair Deal for Guyana campaign said: “In my opinion the government has sold off Guyana’s oil without a care for the environment, without a care for the people, without a care for fishermen and others who stand to lose everything from a spill, without a care for Guyana’s marine environment which could be totally destroyed, without a care for future generations who might inherit nothing but an oil slick, and without any understanding whatsoever of the dangers of climate change. People also have to understand that an oil spill or a well blow-out could harm our Caribbean neighbours and Guyana could be liable for that damage.”

The oil companies oppose the legal claim.