Tullow, with a market cap of $361 million as of Tuesday and $3 billion in debt, said it was looking at "various refinancing alternatives" and plans to hold a capital markets day later this year.

It warned that the process carried uncertainties that could risk its going concern status.

"Cash flow projections forecast a potential liquidity shortfall during the 18-month period relevant to the Liquidity Forecast Test in respect of the January 2021 RBL re-determination due to the maturity of the $650 million Senior Notes due in April 2022," it said.

Tullow, which is slashing jobs and selling assets, said it is looking to refinance convertible bonds due next year or the senior notes due in 2022, amend its reserve-based lending (RBL) facility or raise cash from banks or other investors by January.

Like other oil producers, Tullow has already received debt covenant waivers this year, but Finance Chief Les Wood said Tullow did not take continued waivers for granted.

Tullow reported a half-year loss of $1.3 billion on Wednesday, compared with a $103 million profit last year, as it took an expected $1.4 billion writedown after it lowered its oil price outlook. Tullow has untapped liquidity and around $500 million in available cash.

It plans to spend around $365 million on investments and decomissioning this year. Tullow said it expects its 2020 cash flow to break even at current oil futures prices. It has hedged 60% of its sales this year at a floor price of $57 a barrel and 48% of next year's at a floor of $51 a barrel.

Tullow said it halted the sale of a portion of its Kenyan onshore oilfields pending a review, but is confident it will close the sale of its Ugandan assets for around $500 million this year to France's Total

Its shares were down around 8% at 18 pence at 0818 GMT.

Tullow, founded in the 1980s to tap into African oil and gas, suffered a series of technical difficulties and missed production targets, leading its chief executive to step down late last year.

($1 = 0.7724 pounds)

By Shadia Nasralla