* Pfizer update on coronavirus vaccine sends shares, oil higher

* Soybeans already supported by strong demand, S. America dryness

* Grain markets await USDA supply/demand update on Tuesday

CHICAGO, Nov 9 (Reuters) - U.S. soybean futures reached a new four-year high on Monday as the first successful data from a late-stage COVID-19 vaccine trial fueled hopes of the economy recovering quickly from the pandemic-driven crisis.

Broad optimism about Pfizer's vaccine trials added support to a soybean market already buoyed by strong Chinese demand and weather risks in South America.

The "positive ramifications of Pfizer news today cannot be overstated," said Rich Feltes, a grain analyst and head of market insights for U.S. futures brokerage RJ O'Brien.

The most-active soybean contract on the Chicago Board of Trade (CBOT) ended up 9 cents at $11.10-1/2 per bushel. It earlier rose to $11.18 a bushel, its highest price since July 2016.

Most-active corn futures crawled 3/4-cent higher to $4.07-1/2 per bushel, while wheat slid 4-1/2 cents to $5.97-1/2 per bushel at the CBOT.

Traders adjusted positions in the markets before the U.S. Department of Agriculture (USDA) issues a monthly report on Tuesday that is expected to trim the government's estimates for domestic soybean and corn yields and inventories.

An uptick in demand for U.S. farm products from China, the world's top soybean importer, has helped to draw down U.S. ending stocks.

The USDA, in a daily reporting system for export sales, said on Monday that exporters sold 123,000 tonnes of U.S. soybeans to unknown destinations.

The deal is "a continuation of post-election buying," Feltes said, after the USDA on Friday announced separate U.S. soybean export sales to China and unknown buyers.

The USDA, in a weekly report released after the market closed on Monday, said the U.S. soybean crop was 92% harvested and corn was 91% harvested, compared with expectations for 94% and 91%, respectively. The agency rated 45% of the nation's winter wheat crop as good or excellent, compared with expectations for 44%.

(Reporting by Tom Polansek in Chicago. Additional reporting by Gus Trompiz in Paris and Naveen Thukral in Singapore; Editing by Marguerita Choy)