CHICAGO, Dec 17 (Reuters) - Spot basis bids for corn and soybeans delivered by barge to U.S. Gulf Coast terminals turned higher Tuesday on spot demand and lower futures prices, traders said.

* Chicago Board of Trade soybean futures sank to life-of-contract lows on Tuesday as favorable crop conditions in Brazil and weak Chinese demand for U.S. soybeans hung over the market, traders said.

* The U.S. Department of Agriculture on Tuesday confirmed private sales of 170,400 metric tons of U.S. corn for delivery to Mexico during the 2024/25 marketing year.

* USDA also confirmed private sales of 187,000 metric tons of U.S. soybeans for delivery to Spain, and 132,000 metric tons of U.S. soybeans for delivery to unknown destinations. Both are for delivery during the 2024/25 marketing year.

* Empty barge freight rates are still elevated on parts of the Illinois and Mississippi Rivers due to extended transportation delays, one broker said. But that could change, the broker said, as water levels are rising and shippers are able to load more grain per barge.

* At the Gulf, CIF soybean barges loaded in December were bid at 91 cents over Chicago Board of Trade January futures, up 1 cent from Monday.

* FOB export premiums for January soybean shipments were steady at about 109 cents over futures.

* For corn, CIF barges loaded in December were bid at 69 cents over CBOT March futures, up 1 cent from Monday. January corn barges were bid at 71 cents over futures, up 2 cents; February barges were bid at 73 cents over futures, up 1 cent.

* FOB offers for corn shipped from the Gulf in January held steady at nearly 87 cents over CBOT March futures.

(Reporting by P.J. Huffstutter)

((pj.huffstutter@thomsonreuters.com; 313-484-5275 (w);))

((For displays of CIF basis, click on the codes in brackets:

U.S. CIF Gulf soybeans

U.S. CIF Gulf corn

U.S. CIF Gulf SRW wheat

U.S. CIF Gulf HRW wheat For displays of FOB basis, please click on the following codes in brackets:

U.S. FOB Gulf corn

U.S. FOB Gulf soybeans

U.S. FOB Gulf SRW wheat

U.S. FOB Gulf HRW wheat

LINKS Corn prices page: cpurl://apps.cp./cms/?pageid=corn-cash-market Wheat prices page: cpurl://apps.cp./cms/?pageid=wheat-cash-market U.S. barge freight U.S. export sales estimates U.S. grain export summary Brazil soybean export prices Brazil corn export prices Argentina grain prices Russia grain prices ))