The deal making goes on.

Less than a week after announcing partnerships with

IBM

(IBM) - Get Report

and

i2

(ITWO)

,

Ariba

(ARBA)

on Monday announced partnerships with

American Express

(AXP) - Get Report

and

Dell

(DELL) - Get Report

in the surging B2B space.

In apparently the more important of the two deals, Ariba and American Express will develop a utility that will allow businesses to pay suppliers completely online, by using either a purchase card or through a transfer of funds.

"When you get right down to it, no purchase is truly an online transaction unless payment takes place online as well," said Ed Gilligan, president of American Express Corporate Services. "And even with e-commerce, most companies are still writing each other checks."

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The companies announced the deal at the

Ariba User Group and Advisory Council

conference in San Diego. Ariba makes software that allows companies to easily buy and sell things among one another. American Express is a leading credit card issuer.

"To me, the American Express deal is the bigger one

of the day's announcements," said Bob Austrian, B2B analyst for

Banc of America Securities

, who rates Ariba a strong buy. His firm has not done underwriting for the company. "Every time a transaction happens, it has to be paid for, and what better way to do that than to attack the payments."

In addition to focusing on streamlining payments -- and presumably the companies' ability to grab a piece of them with each B2B transaction -- the deal will introduce the two companies' customers to each other.

It will allow merchants in the

American Express B2B Commerce Network

to do business with companies using Ariba's B2B e-commerce platform. Conversely, it will give Ariba access to American Express' formidable army of corporate customers and merchants who accept the American Express card.

The deal came about in the wake of Ariba purchasing online exchange developer

Tradex Technologies

, which American Express had invested in for its own B2B initiatives. With Ariba now finalizing that acquisition, American Express will now have an equity stake in Ariba.

In the other deal, Dell will invest in Ariba and the companies will be developing a marketplace for small and medium-sized businesses to buy goods over the Internet. The companies also will promote their products in each of their markets.

The size of Dell's investment was not disclosed.

Ariba closed down 7 3/8, or 2.4%, at 291 during today's

Nasdaq

selloff. American Express closed down 1/8 at 126 9/16. Dell was up 3 at 54 3/4.