* Tight supply, good demand lift soybeans to highest since 2016

* Soybean gains helped by soyoil amid tight world vegoil supplies

* Corn boosted by good exports

CHICAGO, Nov 18 (Reuters) - U.S. soybean futures rose to a new four-year peak on Wednesday, led by sharply higher soyoil and as robust demand for beans from exporters and domestic processors fueled worries about tightening supplies of the oilseed.

Corn and wheat followed soybeans higher, with strong export demand giving corn an additional lift.

Grains remain supported by worries about South American crops following dry early-season weather in Argentina and Brazil. Recent rains have alleviated some of the weather stress, but tightening global supplies, particularly of soybeans, have left little room for a crop shortfall.

"Stocks-to-use ratios (for soybeans) tell us we should be higher," said Craig Turner, senior commodities broker with Daniels Trading.

"The U.S. is having to ration exports. And that is a direct function of how many beans South America can produce to make up for either the deficit or abundance of global export supplies between now and next year's U.S. harvest," he said.

Chicago Board of Trade (CBOT) January soybeans were up 6 cents at $11.75-3/4 a bushel after peaking earlier at $11.89-3/4, the highest for a most-active contract since June 13, 2016.

Soyoil futures, which gained more than 2% on Wednesday amid tight global supplies of vegetable oils such as palm and canola, fuelled gains in soybeans.

CBOT December corn was up 5-1/2 cents at $4.25-3/4 a bushel after earlier posting a contract high of $4.28-1/2, the highest for a most-active contract since July 25, 2019. CBOT December wheat gained 2-1/2 cents to $5.98-1/4 a bushel.

Strong U.S. corn export demand and expectations for further large purchases by China supported corn futures.

The U.S. Department of Agriculture on Wednesday said private exporters sold 140,000 tonnes of U.S. corn to undisclosed buyers. That followed recent large corn sales to Mexico and South Korea. (Additional reporting by Nigel Hunt in London and Naveen Thukral in Singapore Editing by David Goodman, Kirsten Donovan and Tom Brown)