Aug 13 (Reuters) -Spot basis bids for soybeans shipped by barge to the U.S. Gulf Coast firmed on Tuesday, while corn bids were steady to lower, as a slump in grain and oilseed prices spurred some spot buyer interest, traders said.

* Chicago soybean futures Sv1 lost more ground on Tuesday, setting another four-year low a day after U.S. Department of Agriculture data reinforced the prospect of a bumper U.S. harvest.

* The U.S. Department of Agriculture (USDA) on Monday confirmed private sales of 132,000 metric tons of soybeans to China for delivery during the 2024/2025 marketing year that begins Sept. 1, 2024.

* USDA also confirmed private sales of 137,160 metric tons of corn to Mexico during the 2024/2025 marketing year.

* As rain fell across parts of the U.S. Midwest, parts of the interior rivers - such as the Mississippi River near the St. Louis area - are showing signs of cutting back drafts, one broker said. Empty barge freight rates have firmed in recent days on anticipated demand and tight supplies ahead of harvest, the broker said. BG/US

* CIF Gulf soybean barges loaded in October traded at 64 cents over CBOT November SX24 soybean futures, traders said. Soybean barges loaded in November also traded at 74 cents over futures.

* CIF Gulf soybean barges loaded in August were bid at 68 cents over CBOT November SX24 soybean futures, up 3 cents from Monday. September soybean barge bids were at 59 cents, and offers down 2 cents at 68 cents, over November futures.

* FOB export premiums for Gulf soybean loadings in the first half of September were down 2 cents at about 108 cents over November futures. Premiums for last-half September shipments were steady, offered at around 87 cents over futures.

* For corn, CIF Gulf barges loaded in August were bid at 57 cents over CBOT September CU24 corn futures, down 1 cent. September corn barges were steady, bid at 68 cents over futures.

* FOB offers for Gulf corn shipments loaded in September were down 2 cents, at about 83 cents over 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