"For the G20 economies, we expect GDP growth of just under 3.0 percent each year in 2015 and 2016, unchanged from 2014 and from our November 2014 Global Macro Outlook," the credit ratings agency said in its latest outlook report.
Low oil prices normally help grease the wheels of business and spur global economic growth, but Moody's said Wednesday it would not revise its forecasts for the G20, citing a variety of offsets to the expected windfalls.
"In the euro area, Japan and Brazil, and some other net oil importers in the G20, the fall in oil prices takes place in an unfavourable economic environment," said Marie Diron, Moody's senior vice president for credit policy.
She pointed to high unemployment and new political uncertainty in some eurozone countries, and to Brazil's tightened monetary and fiscal policy.
"In this context, a large part of the income gains from lower oil prices is likely to be saved rather than spent," Diron wrote.
The Group of 20 includes the leading industrialised and developing nations.
Moody's forecasts GDP growth of under 1.0 percent in 2015 in the eurozone and Japan.
The United States and India "are among the main beneficiaries (among G20 nations) from cheaper oil as consumers and companies spend part of the gains in real income," Moody's said.
The US-based agency forecasts US GDP growth of 3.2 percent in 2015 and 2.8 percent in 2016, while it expects India's economy to grow by nearly 7.0 percent in 2016.
As for oil-producing G20 economies, the price slump will hit Russia hard, worsening the effects of "a pre-existing downward trend in the economy's potential and the geopolitical crisis" surrounding Moscow's role in the Ukraine crisis, Diron said, predicting a "sharp recession" lasting until 2017.
"In Saudi Arabia, higher fiscal spending will mitigate the negative effects of lower oil prices and help to maintain positive growth," she said.
The forecasts are based on an assumption that oil prices will stay at an average of $55 a barrel for Brent in 2015.
Moody's conclusions followed a warning on Tuesday by the International Energy Agency, which said that the net impact of low oil prices "will be more modest than might be expected" because of a lingering hangover from the global economic crisis in 2008 and weak investment.