The company said in a statement Wednesday it had mixed results in frontier basins in Mauritania, Ethiopia and Norway.
"Tullow expects a net exploration write off of $415 million for the first half of the year," it said.
Tullow Chief Executive Officer Aidan Heavey said his company was optimistic in the face of disappointing results elsewhere. There's "significant upside potential" in assets off the coast of Ghana, Kenya and Uganda, he said.
"With potential basin-opening wells across the portfolio coming up in the second half of the year and strong revenue and cash flow, Tullow is in a strong position for the remainder of this year and into 2015," he said in a statement.
Ghana's Jubilee oil field, a centerpiece for Tullow, is producing about 100,000 barrels of oil per day.
The Tweneboa-Enyenra-Ntomme off the coast of Ghana should deliver its first oil by 2016. At its peak, it is expected to produce about 80,000 barrels per day.