The Green Party's calling for Shell Oil to be prosecuted for illegally drilling two wells off the coast of Taranaki.

The Environmental Protection Authority's ruled Shell Todd Oil Services broke the law by drilling wells without a marine consent in May.

Green MP Gareth Hughes says the EPA's own officials have warned that non-compliance will continue unless there are prosecutions.

"It's to be expected that if the EPA's only going to hand them a letter, a slap with a wet bus ticket, people are going to continue to flout and break the law."

Hughes says ultimately responsibility needs to be taken by Shell Oil, but the government's relaxed attitude towards protecting the area is also to blame.

"The government needs to have more oversight, more monitoring of these sites. They've got to have a better handle over the oil and gas sector."