Nov 15 (Reuters) -Basis bids firmed on Friday for soybeans shipped by barge to U.S. Gulf Coast terminals, buoyed by exporter demand for prompt supplies and a slowdown in farmer sales this week as Chicago Board of Trade (CBOT) soybean futures Sv1 retreated back below $10 a bushel, traders said.

* But corn barge bids fell, as did export premiums for both corn and soybeans shipped out of the Gulf to overseas buyers, reflecting a drop in costs for barge freight on Midwest rivers since late October. BG/US

* Increased rainfall this month has lifted water levels on the Mississippi River, hastening the movement of grain barges toward the Gulf and allowing for heavier loads on fewer barges. "The river is in good shape," said one grain merchandiser on the mid-Mississippi River.

* At the Gulf on Friday, CIF soybean barges loaded in November were bid at 88 cents over CBOT January SF25 futures, up 3 cents from Thursday. December soybean barges were bid at 85 cents over futures, up a penny.

* But FOB export premiums for soybeans shipped out of the Gulf in December were around 116 cents over futures, down 1 cent from Thursday.

* For corn, CIF barges loaded in November were bid at 78 cents over CBOT December CZ24 corn futures, down 1 cent from Thursday. December corn barges traded at 81 cents over futures and were re-bid at 80 cents over futures, also down a penny from Thursday.

* FOB offers for December corn shipped out of the Gulf were 2 cents lower at around 110 cents over futures.

* The U.S. Department of Agriculture reported export sales of U.S. corn in the week ended Nov. 7 at 1.315 million metric tons, toward the low end of trade expectations and down 52% from the prior four-week average. EXP/CORN

* The USDA reported soybean sales for the week at 1.555 million tons, in line with expectations but down 24% from the previous week and the prior four-week average. EXP/SOY

* Weekly U.S. wheat sales totaled 380,100 tons, in line with trade expectations for 250,000 to 550,000 tons. EXP/WHE

* On the CBOT, corn and soybean futures rose on Friday on bargain-buying and improving prospects for soyoil demand. GRA/ Still, for the week, CBOT soybeans Sv1 sagged 3.1% and corn fell 1.6%, pressured in part by a strengthening dollar.

Reporting by Julie Ingwersen

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