By Jesse Newman

CHICAGO--U.S. grain and soybean futures posted modest gains as crude oil prices rallied and traders squared positions ahead of the long weekend.

Corn prices rose, buoyed by surging prices for crude oil, which rose 10% on Friday. Higher oil prices often provide a lift to corn and soybean markets, as they encourage refiners to blend alternative fuels--like corn-based ethanol and soybean-based biodiesel--into U.S. supplies of gasoline and diesel.

Trader positioning ahead of the long weekend also boosted corn prices. Investors often exit bearish bets prior to an extended pause in trade in order to minimize risk in case of a major political or macroeconomic event.

"It's a wishy-washy time right now," said Terry Linn, executive vice president at Chicago commodity futures-trading firm and asset manager Linn Group. "There's just not a lot of news to drive the markets."

Corn futures for March rose 1 1/4 cents, or 0.4%, to $3.61 1/2 a bushel at the Chicago Board of Trade.

Soybean prices nudged higher, bolstered by sharp gains in the energy markets. Analysts said rising soybean oil prices also propped up the prices for the oilseeds. Prices for soybean oil gained 0.7% on Friday, benefiting from higher prices for rival palm oil, which have increased thanks to lower-than-expected output in Malaysia.

"El Nino has hurt production in the palm market in the far east, which has been a big driver" of soybean oil prices, said Mr. Linn.

Still, soybean prices were pressured by crop-friendly weather in South America, a major U.S. rival for soybean production and export. The advancing soybean harvest there also weighed on prices for the oilseeds, with farmers reporting better yields as they fieldwork progresses.

CBOT March soybeans added 1/2 cent, or 0.03%, to $8.73 3/4 a bushel.

Wheat prices inched upward, supported by signs of world demand for the grain and concerns over winterkill in the Black Sea region, where dropping temperatures could harm dormant wheat plants not sufficiently insulated by the snow. Egypt, the world's largest wheat buyer, bought 60,000 metric tons of Romanian wheat on Friday, indicating the country's continued need for supplies.

Uncertainty over Egypt's standards on the potentially dangerous ergot fungus still is hampering the wheat trade, however, with many regular suppliers declining to make offers in the international tender due to concerns over Egypt's quality-control standards.

CBOT March wheat moved upward by 1/2 cent, or 0.1%, to $4.58 3/4 a bushel.

Write to Jesse Newman at jesse.newman@wsj.com

(END) Dow Jones Newswires

February 12, 2016 12:14 ET (17:14 GMT)