Exxon Mobil Corporation has been looking to buy renewable energy for delivery in Texas, according to people familiar with the matter.

The largest US oil firm sent out a request for proposals with a June 8 deadline, inviting solar or wind power suppliers to pitch contracts that would last 12, 15 or 20 years, according to a document obtained by Bloomberg and people with knowledge who asked not to be named discussing confidential matters.

Exxon, based in Irving, Texas, is seeking at least 100MW and would consider proposals for more than 250MW.

"I have never seen an oil and gas company doing a corporate PPA anywhere near that size," said Kyle Harrison, an analyst at Bloomberg NEF, referring to the power-purchase agreements used to buy electricity. "If you’re seeing the biggest oil and gas companies going out and making investments in clean energy, it shows that renewables are cost competitive. This can be a way for them to show a commitment to sustainability without suffering economically."

Exxon declined to comment.

It is not clear whether the company has reached an agreement with any supplier to buy this power, nor whether it was seeking the electricity for its own use.

Exxon has been slow to follow rivals such as Royal Dutch Shell and BP into renewable energy technologies. While CEO Darren Woods acknowledges the "risk of climate change" and is testing biofuels made from algae for an industrial scale, he said earlier in 2018 that the company’s investment dollars will follow oil magnate John D Rockefeller’s bet-on-what-you-know mantra.