Mr Swindells has been replaced by chief operating officer Andrew Nunn, who praised his former boss for leading Deltic through some of the toughest and most volatile times he had experienced in the industry.
Deltic’s shares plunged around 20% following the announcement of Mr Swindells’ departure, to new lows.
The shares have fallen by almost 95% over the last two years.
The fall reflects a big change in the outlook for North Sea firms since the windfall tax was introduced in 2022.
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The former Conservative Government imposed the tax after North Sea firms enjoyed a huge boost to their profitability from the surge in oil and gas prices triggered by Russia’s war on Ukraine.
Deltic was riding high in the months before the tax took effect.
The company shot to prominence after making the bumper Pensacola find on a North Sea licence that it persuaded Shell to buy into.
The success highlighted the role played by minnows such as Deltic in raising awareness of the remaining exploration potential in the mature North Sea.
Deltic used new technology to help identify prospects that had been missed by others.
However, the company was left facing huge challenges as interest in North Sea exploration and development activity evaporated amid tax increases and the prospect of more to come.
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In June Deltic withdrew from the Pensacola licence after it was unable to raise the funds needed for its share of the work on the prospect despite an “exhaustive effort”.
It cited “deteriorating sentiment towards the oil and gas industry as a result of ongoing fiscal volatility and negative political rhetoric in the run-up to the July election”.
The Labour Government has said it will increase the windfall tax rate by three percentage points and will cut related allowances. Chancellor Rachel Reeves will announce her Budget on October 30.
The rate of the windfall tax was increased from 25% to 35% in November 2022. That took the headline tax rate payable by North Sea firms to 75%.
On Monday Aberdeen and Grampian Chamber of Commerce said confidence had fallen to a record low in the North Sea.
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Mr Nunn said Deltic’s small team had delivered what would have been, at any other time in the industry’s history, a company-making success with the Pensacola discovery.
Deltic still hopes to be able to make money in the North Sea. The company is drilling a well on the Selene prospect, which it encouraged Shell and Korean-owned Dana Petroleum to invest in.
However, Mr Nunn said Deltic planned to look further afield to find value for shareholders.
He noted: “We anticipate shortly announcing a series of measures to reduce the Company’s overheads.”
Deltic shares sold for 4.25p yesterday, compared with around 80p in September 2022.
Mr Swindells entered the oil and gas industry after studying accountancy at the University of Glasgow. He became finance director of Deltic in 2013 and was promoted to the chief executive’s post in 2018.
