It might have been a first: a large multinational oil company launching an ad campaign in which it admits to "abuses that companies usually try to hide".

Not so fast. In an elaborate hoax, pranksters on Monday pre-empted Chevron's latest advertising campaign "we agree" with a series of spoofs that appear to have fooled some news outlets.

"Chevron is making a clean break from the past by taking direct responsibility for our own actions," an official was falsely quoted as saying on a mock Chevron website.

"For decades, oil companies like ours have worked in disadvantaged areas, influencing policy in order to do there what we can't do at home. It's time this changed."

The hoax, which was reportedly carried out by environmental groups and the Yes Men group, also lampooned Chevron's rival, BP.

"BP's response to the Gulf tragedy was widely perceived as perfunctory and insincere," the text noted, adding that "oil companies should clean up their messes."

Unsurprisingly, Chevron was not very happy, calling the ads "environmentalist subterfuge".

"Earlier today, a group of environmentalists cyber-posing as Chevron officials illegally spoofed Chevron's just-launched 'We Agree' advertising campaign," the real firm said in a statement.

"Chevron does not take this attack lightly," said Hewitt Pate, Chevron's top lawyer. "We invest extremely heavily in our campaigns and we take them extremely seriously. Such actions can never be tolerated."

The company spends at least $US90 million ($A91.18 million) a year on advertising.

The fake campaign made heavy references to Chevron's legal woes in Ecuador, where the company is being sued over massive environmental contamination in the Amazon jungle.

Some 30,000 Ecuadorian plaintiffs are suing Chevron for allegedly pouring billions of gallons of toxic waste into the rainforest.

The company said it had "binding agreements with the Ecuadorian government exempting us from any liabilities whatsoever".