North Sea-focused oil and gas firm Ithaca Energy posted a loss last year of more than £400m, after taking a huge hit on the value of its assets.
Ithaca saw total production more than double in 2020 to 24.3 million barrels.
Revenues almost doubled to £850m after it bought Chevron assets in the North Sea in late 2019.
But it took a pre-tax impairment of £495m on its oil and gas assets as a result of a sharp fall in commodity prices in the early part of last year.
Israeli-owned Ithaca has interests in 17 producing fields, which mainly lie in the Central North Sea area of the UK Continental Shelf.
Last year's output was boosted after the Vorlich field in the Greater Stella Area, in which it has a 34% working interest, was successfully brought on stream in the fourth quarter.
In its results statement, Ithaca stated that the business had performed well in a "challenging environment" by responding quickly to "mitigate the operational and financing risks of Covid-19 and lower oil prices".
It added: "Despite the sharp reduction in prevailing commodity prices, the group still generated significant free cash flow in 2020 as a result of production results, a competitive cost base and a strong commodity hedging position."
According to the company, it had total proven and probable reserves and resources of 298 million barrels of oil equivalent as of 31 December.
During the year it reduced its net debt from nearly £1.1bn to less than £870m.
Meanwhile, a new name in offshore production started share trading on Thursday.
Harbour Energy was formed from the merger of Chrysaor and Premier Oil, making it the biggest UK-based independent producer in UK waters, at more than 160,000 barrels per day.