Sept 18 (Reuters) -Basis bids for corn shipped by barge to the U.S. Gulf Coast were flat to lower on Wednesday after spiking earlier in the week on rising freight costs, traders said.

* CIF soybean basis bids were steady to firm, although nearby values were at a steep discount to deferred bids as rising supplies from the Delta region harvest weighed on the market. Bids for November barges were strong as traders anticipated good export demand and tighter available supplies as the harvest winds down.

* China's return from the mid-autumn festival holiday is expected to spark some soy buying by the world's top importer for November and December shipment, traders said.

* Low water on the lower Mississippi River impeded barge shipments to the Gulf and kept a firm floor under freight costs. Barge lines are limiting drafts and tow sizes, which is increasing the per-bushel cost of shipping.

* The Mississippi River at Memphis is forecast to fall to within 3 feet of its all-time low by the end of this month, according to National Water Prediction Service data.

* CIF corn barges loaded in September were bid 2 cents lower at 71 cents over Chicago Board of Trade December CZ24 futures. October barge bids were down 2 cents at 76 cents over futures.

* FOB Gulf export premiums for corn shipped in November, the earliest available loading slot, were up 2 cents at 112 cents over CBOT December futures.

* CIF September soy barges were bid 2 cents higher at 65 cents over CBOT November soybean SX24 futures, while October barge bids gained 1 cent to 71 cents over futures.

* FOB soy export premiums for the first half of November were steady at around 130 cents over futures, while last-half November offers were up 2 cents at 118 cents over futures.

Reporting by Karl Plume in Chicago; Editing by Jamie Freed

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