Barge freight rates on the Mississippi River at St. Louis were higher amid demand from shippers, while bids on the Illinois and lower Ohio rivers were lower on slow movement.
Traders said there was export demand for corn from regular buyers like Mexico, Japan and Latin American importers.
"There's interest from Japan," a trader said, adding that South Korea has been buying corn for shipment from the Pacific Northwest because of lower freight to Asia.
Another trader said farmer selling of corn was generally slow because of low prices in the cash market.
"They can get nearly $3.00 (a bushel) for their corn if they deliver it in June," he said, adding that the price included benefits from government programs.
Soyabean basis offers were firms in line with gains in the CIF barge market amid demand from exporters, traders said.
There was talk of demand from China, but any deals could not be confirmed by traders said.
Hard and soft red winter wheat basis offers were mostly steady in the FOB market, traders said.
Traders were getting anxious over the absence of any sales to Iraq, whose deputy prime minister said early this month that the country would buy one million tonnes of US wheat.
"I think they have not yet worked out the final details yet," a trader said. "Negotiations are probably going on."
There were rumours in the market that Iraq would buy 800,000 tonnes of US wheat, traders said.