The company reported losses of 37.5 billion kroner (3.96 billion euros, $4.39 billion) last year compared to profit of 21.9 billion kroner in 2014.
The group -- 67 percent-owned by the Norwegian state -- said it would slash its investments this year by $3.5 billion to $13 billion.
For the fourth quarter, net losses rose to 9.2 billion kroner from 8.9 billion a year earlier.
"The result in the fourth quarter is highly impacted by the weak commodity price," Statoil CEO Eldar Saetre said in a statement.
"However, we continue to make strong progress on costs and efficiency. We are now further stepping up our improvement programme, and tightening our capital and exploration expenditures. These are key elements in navigating the business during a period of low oil prices".
Oil companies have been downsizing staff and mothballing drilling rigs in response to a drop in oil prices from more than $100 a barrel in July 2014 to about $30 a barrel currently.
Statoil has placed a lot of hope in the massive Johan Sverdrup oil field in the North Sea, which is expected to begin operations in late 2019 and whose development costs have been reduced by seven percent.
But the group has postponed until the second half of 2018 the start of operations on the Aasta Hansteen field in Norway and the Mariner field in Britain.
They had been expected to open in 2017.
The delays are bad news for the Norwegian economy, which relies heavily on the oil sector.