The EU's incoming energy and climate commissioner said on Tuesday he is selling his shares in oil firms to avoid any conflict of interest ahead of a grilling by the European Parliament.

Spain's Miguel Arias Canete was named last week by Jean-Claude Juncker, who takes over as head of the European Commission in November, as part of the new team that will lead the EU's executive branch.

But all 27 commissioners nominated by Juncker face tough questioning by European legislators in interviews from September 29 until October 7, before the parliament votes on the whole team on October 22.

Canete, the former Spanish agriculture minister, has in particular faced criticism for his shares in energy companies and separately over allegedly sexist comments.

"I gave instructions to divest my shares in the energy sector the moment I was nominated... to avoid even the slightest notion of potential conflict of interest", Canete said in a statement released by the parliament's dominant centre-right European People's Party conservative bloc, of which he is a member.

He said the sale of his shares in the Petrolifera Ducar and Petrologis Canarias oil storage firms will be completed by Thursday.

Canete declared in June that his shareholdings in the two firms were worth around 326,000 euros ($423,000) in 2011.

The energy and climate job is an important one, with the Ukraine crisis threatening Europe's gas supplies from Russia.

Canete has faced pressure from the environmental group Greenpeace to settle his "conflict of interest" and improve his environmental record.

He also sparked controversy when he implied he had "intellectual superiority" over a "helpless" female socialist rival during the campaign for the European elections in May. He was forced to apologise.

The chairman of the socialist group in the European Parliament, Gianni Pittella, said Canete had a possible "conflict of interest" and said all candidates would face a tough grilling over their professional competence and ethical standards.

The co-chairman of the Greens Group in parliament, Rebecca Harms, promised Canete would face a particularly tough hearing, alluding to the sexist remarks he made.

Incoming economic affairs commissioner, France's former finance minister Pierre Moscovici, and Britain's Jonathan Hill, given the financial services brief, are also both set for a grilling according to Philippe Lamberts, the co-chairman of the Greens.

But the nominee that "concerns us the most" is Hungary's Tibor Navracsics, whom Juncker named for the education, culture, youth and citizenship post, said Pittella.

Navracsics is close to Hungary's Prime Minister Viktor Orban, whose relations with the EU are strained because of his crackdown on the courts, the media and non-government organisations.