Goldman Sachs has slashed its 2015 oil price forecasts, making it the most bearish among major financial institutions, following a near 25 percent fall in crude prices over the past five months. The U.S. investment bank said rising output will outstrip demand—with its forecast weighing further on benchmark crude prices—as forecasters generally pare back estimates for oil due to global growth, a strengthening dollar and ample supplies. Goldman analysts said in a report released late on Sunday that it expects U.S. benchmark West Texas Intermediate crude to fall to $75 a barrel and Brent to $85 a barrel in the first quarter of 2015, both down $15 a barrel from its previous forecast. WTI could fall as low as $70 in the second quarter and Brent as low as $80, when oversupply would be the most pronounced, before returning to first-quarter levels, Goldman said.

Pump jacks and wells on the Monterey Shale formation in California David McNew / Stringer | Getty Images News

Goldman's projections contrast with those of Standard Chartered Bank's oil analyst Paul Horsnell, known for having called the market's long rally a decade ago, who is sticking with a more bullish bias. Read MoreU.S. gasoline cheapest in nearly four years -Lundberg survey

Last week, Horsnell and his team cut their first quarter Brent forecast to $98, but pared back their forecast for calendar 2015 by just $5 to $105 a barrel. Brent crude futures dipped 0.2 percent on Monday to below $86 a barrel, extending their decline despite a continued easing of worries over the global economic recovery, said Tomomichi Akuta, senior economist at Mitsubishi UFJ Research & Consulting.

"I personally think prices have room for declines though not as steep as Goldman," Akuta said. NYMEX crude for December delivery was up 4 cents at $80.05 a barrel by 0104 GMT, after settling down $1.08 on Friday following a spike up on Thursday. Rising Output Goldman said production outside OPEC countries was expected to accelerate, led by Brazil and drilling in the Gulf of Mexico with the end of extensive deep-water maintenance following the 2010 Macondo disaster. Read More Oil could slide further, but where's the bottom?

Non OPEC-production outside the U.S. Lower 48 states is forecast to increase by 412,000 barrels per day this year, 573,000 bpd in 2015 and 505,000 bpd in 2016. Output from Brazil's Santos basin is forecast to start to pick up, increasing Brazilian output by 206,000 bpd in 2014 and 325,000 bpd next year. Gulf of Mexico production is expected to increase by 155,000 bpd in 2015.