Irish-founded oil and gas explorer Tullow has announced revenues of $1.6 billion for 2015, down 27 per cent on the $2.2 billion recorded a year earlier.

The group attributed the decline in revenues to a mixture of write-offs, impairment charges and the global oil price decline, all of which led to a $1.03 billion after-tax loss, down 37 per cent on the $1.6 billion loss seen in 2014.

Tullow reported its first ever loss in 2014 due to significant write-offs, impairments charges and a 16 per cent decline in revenues.

Pre-tax operating cash flow of $1 billion, down 38 per cent compared to a year earlier. Year-end debt for the group stood at $4 billion with free cash of $1.9 billion.

Writedowns made last year included an exploration pre-tax write-off totalling $749 million, a pre-tax impairment charge of $406 million and a service contract charge of $186 million.

Tullow, which is listed on the London, Irish and Ghanaian stock exchanges, has interests in over 125 exploration and production licences across 22 countries.

Group production in 2016 is expected to average 82.500 barrels of oil equivalent per day (boepd), up 12 per cent on last year the group said. The company’s flagship TEN project is now over 85 per cent complete with first production anticipated in July or August.

Capital expenditure has been maintained at $900 million to $1.1 billion for the year, although Tullow said it could reduce capex to around $300 million for 2007 onwards if necessary.

"In the year ahead, we have three key priorities: ensuring continued low cost production from West Africa - including the start-up of production from TEN between July and August 2016; driving further reductions in operating costs and capital expenditure; and focusing on deleveraging the balance sheet through free cash flow generation and strategic portfolio management," said chief executive Aidan Heavey.

“As we look ahead, we have a portfolio of world class, low cost oil assets which will produce around 100,000 bopd in 2017 and a major position in one of the world’s newest, low cost, oil provinces in East Africa, both enabling us to create substantial value,” he added.

Smurfit shares were up 4.6 per cent in early trading in Dublin and rose 2.7 per ent in London on Wednesday.