Gazprom Neft Deputy General Director Vadim Yakovlev said the forecast had been cut due to falling oil prices and unsuccessful geological prospecting at some oil deposits.
Yakovlev said the company expected its oil output to decline in 2009 compared with this year.
"Now we are calculating what the reduction of crude output will be with less investment," he said.
Gazprom Neft will cut its investment program by up to a quarter in 2009 to around 70 billion rubles ($2.59 billion), Yakovlev said.
"Investment will decline 20-25% in 2009. If oil prices fall further, the reduction [of the investment program] will be larger," Yakovlev said.
The executive said Gazprom Neft's investment program for 2008 stood at 85-90 billion rubles ($3.1-3.3 billion).
Yakovlev said investment program reductions would involve projects that had no serious effect on crude output, although he added that output in the Russian oil industry was expected to decline 5% in 2009.
Russia's Energy Ministry predicts the country's oil production to fall from 491 million tons (3.6 billion barrels) in 2007 to 490 million tons (3.59 billion barrels) in 2008 or 0.3-0.4%.
Gazprom Neft has filed a request to Vnesheconombank for a loan to refinance its foreign liabilities but has not revealed the exact sum.
