Shell Petroleum Development Co., a Shell consortium in Nigeria, said oil and gas production in the oil-rich African nation was "significantly lower" than 2005, The Wall Street Journal reports.
Militants in the Niger Delta region stepped up attacks on oil infrastructure after 2005, the Journal adds.
"We undoubtedly had a difficult year in Nigeria in 2009," said Shell Chief Executive Peter Voser in the report. "The Niger Delta remains a very challenging place in which to operate. Security issues and sabotage are constant threats to our people, assets and the environment."
Meanwhile, several Nigerian nationals are suing shell in a Netherlands court, saying oil spills from Shell infrastructure is hurting their livelihood.
Shell said more than 100,000 barrels of crude oil were lost to spills in the Niger Delta in 2009, double the 2008 volume and four times the 2007 total, the Journal said.
The oil company said sabotage, oil theft and militant activity was in part to blame.