July 24 (Reuters) -Spot basis bids for corn and soybeans shipped by barge to U.S. Gulf Coast terminals firmed on Wednesday, traders said.

* Chicago wheat and corn futures gained strength on Wednesday as the market monitored a hot, dry spell forecast in parts of North America, but gains were capped by sizeable global supplies.

* Nearby empty barge freight rates along the Illinois River - which has been surging in recent weeks - eased back slightly late Tuesday and continued to turn lower on Wednesday, traders said.

* But rates are expected to stay somewhat elevated in the near-term, as barge freight supplies have been tight in the wake of lack of access to parts of the mid-Mississippi River, traders said. BG/US

* "It's been causing all sorts of headaches, and having an impact on prices," one broker told Reuters.

* Weather issues also have caused some loading snarls down in the Delta region, one trader said, as strong storms have been moving through the region this week.

* CIF corn barges loaded in July were bid around 69 cents over Chicago Board of Trade September futures CU24, up 3 cents. Barges loaded in August were bid about 70 cents over futures, up 2 cents.

* FOB offers for corn shipments loaded from the Gulf in August were steady at around 78 cents over September futures. Premiums for deferred months also remained steady, though a trader said the market has become volatile as importers need supplies.

* CIF soybean barges loaded in July were bid at 79 cents a bushel over CBOT August futures SQ24, up 1 cent from Tuesday. Bids for August barge loadings were 66 cents over futures, up 4 cents.

* FOB export premiums for soybean shipments loaded from the Gulf in August were steady at around 87 cents over CBOT August futures.

Reporting by P.J. Huffstutter; 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