Oil giant BP boss Bob Dudley has warned there are big uncertainties for the company over the possibility of Scotland becoming independent. Mr Dudley told the BBC the question mark over which currency Scotland might adopt if there was a 'yes' vote in September's referendum was a concern.
However, Mr Dudley emphasized the firm was continuing to invest in Scotland.
Separately, BP reported a fall in profit for 2013.BP plans to invest £10bn in the North Sea between 2011 and 2016, its highest ever investment in the region.
We have a lot of people in Scotland. We have a lot of investments in Scotland. My personal view is that Great Britain is great and it ought to stay together, added Mr Dudley.
Alistair Darling, head of the Better Together campaign, said Mr Dudley's comments marked the biggest intervention by a major business so far in the referendum debate.
I hope that more companies and business leaders speak out over the coming weeks and months. This debate is far too important to be left to politicians alone, he added.
However, the pro-independence Yes Scotland campaign dismissed Bob Dudley's remarks. With independence, the continued use of sterling has the overwhelming support of the people of Scotland and the public in the rest of the UK, a spokesman said.
Scotland's first minister, Alex Salmond, said that Mr Dudley was entitled to his personal opinion but added that many other chief executives were firmly in favor of independence. He said he would continue to co-operate with BP.
Meanwhile, the firm said that underlying replacement cost profit - which strips out one-off gains and the effect of oil price movements - was $13.4bn last year, down from 17.1bn in 2012.
BP said lost income from asset sales, weaker margins on refining and higher exploration write-offs were to blame. For the final three months of last year, BP said underlying replacement cost profit fell to 2.8bn from 3.9bn. The result for the third quarter was just above average analyst forecasts for 2.7bn.
Including the impact of the asset sales and one-off gains, BP said replacement cost profit for the year more than doubled to 23.7bn compared with$11.4bn in 2012. This was largely thanks to the one-off gain from BP's 17bn sale of its interest in the joint venture TNK-BP, which it sold to Russia's Rosneft.
BP has sold off 38bn worth of assets since the Deepwater Horizon oil spill in the Gulf of Mexico, helping it to fund compensation payouts. However, this sell-off has hit production. BP said it expected reported production to be lower in 2014 due to the sales. The oil firm said in October it still plans to sell off a further 10bn worth of assets by the end of next year.