Aug 28 (Reuters) -Spot basis bids for soybeans shipped by barge to the U.S. Gulf Coast were mostly steady on Wednesday, as lower water levels on the Mississippi River sparked concerns about a third straight year of harvest-season transportation disruptions, traders said.

* Spot basis bids for corn shifted from being priced over the Chicago Board of Trade's September corn CU24 contract to the December corn CZ24 contract, they said.

* The U.S. Department of Agriculture (USDA) confirmed private sales of 165,735 metric tons of U.S. corn to Mexico and another 100,000 tons to Colombia, all for delivery in the 2024-25 marketing year that begins Sept. 1.

* The USDA also confirmed private sales of 264,000 metric tons of U.S. soybeans to China for delivery in the 2024-25 marketing year that begins Sept. 1.

* CIF Gulf soybean barges loaded in last-half September traded at 77 cents over CBOT November soybean SX24 futures. October loadings traded at 79 cents, 80 cents, and 81 cents over November futures.

* CIF Gulf soybean barges loaded in November traded at 86 cents over November futures, and January loadings traded at 74 cents over CBOT January soybean SF25 futures.

* CIF Gulf soybean barges loaded in August were bid down 1 cent at 65 cents over CBOT November soybean SX24 futures. September soybean barge bids were steady at 70 cents over November futures.

* FOB soybean export premiums for early September loading at the Gulf were steady at around 107 cents over November futures. Last-half September shipments were up 2 cents to about 100 cents over futures.

* CIF Gulf corn barges loaded in August bid at 62 cents over December corn futures, while September corn barges bid at 64 cents over December futures.

* FOB Gulf September corn export premiums were steady at about 95 cents over CBOT September futures, while October export premiums also were steady at about 102 cents over CBOT December futures CZ24.

Reporting by P.J. Huffstutter; Editing by Richard Chang

For displays of CIF basis, click on the codes in brackets: U.S. CIF Gulf soybeans GRYM U.S. CIF Gulf corn GRYN U.S. CIF Gulf SRW wheat GRYO U.S. CIF Gulf HRW wheat GRYP
For displays of FOB basis, please click on the following codes in brackets: U.S. FOB Gulf corn GRZC U.S. FOB Gulf soybeans GRZD U.S. FOB Gulf SRW wheat GRZE U.S. FOB Gulf HRW wheat GRZF 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 BG/US
U.S. export sales estimates USDA/EST
U.S. grain export summary GRA/U
Brazil soybean export prices SYBS
Brazil corn export prices SYBX
Argentina grain prices GRA/ARG
Russia grain prices GRA/RU