Martijn Rats, an energy research analyst at Morgan Stanley, was quoted in The Daily Telegraph newspaper in London as saying that an expected settlement would add $13 billion to the company's expenditures for the 2010 oil spill.
Rats said there could be a level of "uncertainty" over the outcome of the trial, scheduled for Feb. 27 at a federal court in New Orleans.
"Given the large amounts involved, we believe both BP and the (Justice Department) will find the associated risk unattractive," he said.
Rats said the settlement with the U.S. government could put the total bill for BP at more than $50 billion.
Most of the companies involved with the Deepwater Horizon oil rig blamed each other for the disaster in which 11 workers died and a huge oil spill resulted. A U.S. government investigation concluded BP, Transocean and Halliburton committed a series of regulatory violations at the site.
A report from U.S. regulators determined the blowout that led to the explosion that sunk the rig came from the failure of a cement barrier. Halliburton manufactured a cement cap for the well and BP aims to sue the company over the disaster.