Oct 22 (Reuters) -Spot basis bids for soybeans and corn shipped by barge to the U.S. Gulf Coast and loaded for export continued to rise on Tuesday on demand from importers, traders said.

* Weak corn prices are fueling a flurry of U.S. export sales while U.S. soybean export premiums are at their highest in 14 months ahead of the U.S. presidential election.

* The U.S. Department of Agriculture confirmed private sales of 359,500 metric tons of U.S. corn to Mexico, the latest of a series of daily corn sales announcements.

* Traders are monitoring low water levels on the Mississippi River that are limiting the amount of cargo per vessel during massive corn and soy harvests.

* A lack of water has narrowed the shipping channel in some areas, limiting the number of barges that can be attached together to form a single flotilla or tow, according to the Soy Transportation Coalition. Tow sizes are being reduced from 10%-15% to 30%-40%, the industry group said.

* CIF October soybean barges traded at 127 cents over Chicago Board of Trade November SX24 futures, 4 cents higher than Monday.CIF November soybean barges were bid 107 cents over CBOT November SX24 futures.

* FOB offers for November soybean shipments rose 1 cent to 136 cents over futures.

* For corn,CIF October corn barges were bid at 94 cents over Chicago Board of Trade December corn CZ24 futures and November barges were bid at 91 cents over futures.

* FOB Gulf offers for November and December corn shipments each rose 5 cents to 120 cents over futures.

Reporting by Tom Polansek; Editing by Mohammed Safi Shamsi

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