NEW YORK (Reuters) - U.S. renewable fuel credits rose to multi-month highs on Friday on increased demand from refiners trying to comply with mandates and higher prices for soyoil, surprising traders who expected Donald Trump's reelection as U.S. president to weigh on the market.

Rising prices for the credits, also called Renewable Identification Numbers (RINs), are welcome news for biofuel producers who depend on them to make up for high output costs. However, they also worsen the pain for petroleum refiners whose profit margins have slumped sharply this year due to oversupply and weak demand.

Prices for both the D4 RINs, issued to biomass-based diesel producers, and the D6 RINs, issued to ethanol suppliers, rose as high as 79 cents each on Friday, traders said.

Those are the highest levels since January, according to LSEG data.

The U.S. government mandates mixing of low-carbon fuels in the country's transportation fuel mix, and issues RINs to companies supplying them. Refiners who do not meet their targets can buy RINs from others or risk fines.

Trump's victory in this week's U.S. elections had led to speculation that small refineries will find it easier to get exemptions to their RIN generation targets under his administration, OPIS analyst Tom Kloza said.

However, Trump has not yet outlined any plans to do that.

"There's uncertainty around whether Trump will reintroduce widespread small refinery exemptions, so some small refiners may be buying now to avoid being caught short," said Alex Hodes, analyst at energy brokerage StoneX.

Market participants also expect fewer RINs to be available for trade next year, partly due to tighter government mandates and weak fuel demand reducing renewables blending, said Will Faulkner, founder of industry analysis firm Carbon Acumen.

Meanwhile, soybean oil prices have also rallied this week on expectations that Trump could impose tariffs on imports of biofuel feedstocks.

Higher prices for feedstocks erode producer margins, making them price their RINs higher, said Paul Niznik, director of energy at consultancy firm Capstone.