BP boss Bob Dudley has said the UK would be worse off if it were to leave the European Union.
With the Prime Minister set to call on businesses to support the case to stay in a reformed EU at the World Economic Forum in Davos on Friday, Mr Dudley said investment in the energy sector would suffer as a result of leaving the Union.
He said that many of the rules that some Brits are unhappy with would still apply even if the UK left, and Britain would lost its influence on the global stage.
Speaking to the BBC, the BP chief executive said: "I think many of the trade regulations would still apply even if Britain were outside of [the European Union].
"And then it would be potentially worse being outside of it.
"I think also Britain's role in the world in terms of influence - it will have more influence being a part of Europe.
"There are lots of technical tax reasons, trade flows, regulation, that would make it better for our business and the energy business in general, the oil and gas business, [if the UK] were a part of Europe."
When asked if remaining the EU would be good for the UK, Mr Dudley said: "I would say yes, most certainly.
"I would also say that I am very supportive of the Prime Minister's efforts to talk with Europe to make it more competitive.
"Because I think Europe can be more competitive...I think it is important for Britain as a trading partner with Europe. I think Europe needs Britain.
"Britain is the fifth largest economy in the world, so I am reasonably hopeful of some changes and some reforms that would come about."
Those in favour of the so-called 'Brexit' claim the UK would actually be able to boost trade around the world, as a result of being less restricted by EU laws and regulations.
But Mr Dudley suggested that leaving the EU would create uncertainty over its investment in the UK.
He added: "I think uncertainty always changes what businesses do.
"And if certain events unfolded that made it more uncertain on the future of those investments and the viability then we would have to look at it carefully.
"But right now we are a long way from that.
"I actually believe that the Prime Minister will secure some reform and I think Britain will its role in the world."