July 3 (Reuters) -Basis bids for soybeans and corn shipped by barge to U.S. Gulf Coast terminals declined slightly on Wednesday in thin trade ahead of Thursday's Fourth of July holiday, traders said.

* High water and flooding continued to impede the loading of grain barges along upper portions of the Mississippi River. Locks 11, 12, 14, 16 and 17 on the Mississippi were closed on Wednesday due to flooding and several others were likely to close by this weekend, according to a U.S. Army Corps of Engineers website.

* However, weak exporter demand for grain at the Gulf muted the impact of the flooding, traders said.

* CIF basis bids for soybean barges loaded in July were quoted at 73 cents a bushel over Chicago Board of Trade (CBOT) August SQ24 futures, down 2 cents from Tuesday.

* FOB export premiums for soybean shipments loaded from the Gulf in August were quoted at around 88 cents over CBOT August futures, also down 2 cents from Tuesday.

* For corn, CIF barges loaded in July were bid around 53 cents over CBOT September CU24 futures, compared with Tuesday's bid of 57 cents over July CN24 futures. The 4-cent drop in the basis was greater than the 2-cent spread between the underlying July and September futures contracts, in effect weakening the basis by 2 cents.

* FOB offers for corn shipments loaded from the Gulf in July were unchanged at around 61 cents over CBOT July futures and premiums for August loadings held at around 63 cents over September futures.

* The U.S. Department of Agriculture (USDA) confirmed private sales of 110,100 metric tons of U.S. soybeans to undisclosed destinations, split between old- and new-crop supplies.

* Ahead of the USDA's weekly export sales report, which is delayed until Friday due to Thursday's holiday, traders expect the government to report export sales of U.S. old-crop corn in the week ended June 27 at 500,000 to 900,000 metric tons.

* Traders estimated old-crop soybean sales at 200,000 to 600,000 tons, and new-crop wheat sales of 350,000 to 700,000 tons.

Reporting by Julie Ingwersen; Editing by Alan Barona

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