As Amazon.com Inc. grew total net sales to $136 billion last year, the increase coincided with an ongoing surge in commerce at Amazon Business, its site catering to companies that sell to other businesses.

The retailer, which has said that Amazon Business surpassed $1 billion in sales while growing 20% month-to-month in its first year of operation ended last April, didn’t break out financial figures for the business-to-business site for the fiscal year ended Dec. 31. But an Amazon spokeswoman said today that the number of third-party sellers on the B2B site has reached 45,000, up about 50% from the approximately 30,000 sellers Amazon said it had at the end of the second quarter ended June 30.

The spokeswoman also noted that Amazon Business has 400,000 customer accounts, representing the buyers on the site, the same figure it noted in June. The B2B site, at Amazon.com/business, has “millions of products” listed for sale, she added.

To help spur the number of transactions on the B2B site, Amazon has enhanced functionality and run promotions geared to business buyers and sellers. Last month, it launched a feature that lets registered buyers establish designated delivery and payment terms for specific groups of buyers within their company’s Amazon Business account, a process that “can cut the number of checkout steps in half,” Amazon Business product manager Jimin Patel says in a blog post.

Amazon Business also launched last month a Back to Business promotion—running from Jan. 16 through Feb. 26—offering savings on more than 6,000 products, including I.T., office and industrial supplies. Brands participating in the promotion include HP, Microsoft, Symantec, Brother Printers, Kimberly-Clark Professional and Rubbermaid.

Amazon Business is No. 104 in the B2B E-Commerce 300.

For the fourth quarter ended Dec. 31, Amazon reported:

Total net sales of $43.74 billion, up 22.3% from $35.75 billion a year earlier;

A 24.6% increase in North American electronics and general merchandise sales, which includes sales of industrial products, to $21.59 billion from $17.33 billion a year earlier;

A 46.9% increase in sales through Amazon Web Services, Amazon’s cloud technology and services business, to $3.54 billion from $2.41 billion;

A 55.4% increase in net income to $749 million from $482 million.

For the full year, Amazon reported:

Total net sales of $135.99 billion, up 27.1% from $107.01 billion in   2015;

A 28.8% increase in North American electronics and general merchandise, which includes sales of industrial products, to $64.89 billion, up from $50.40 billion;

A 55.1% increase in Amazon Web Services sales to $12.22 billion, up from $7.88 billion;

Net income to $2.37 billion compared with net income of $596 million;

Spending on marketing increased 37.7% to $7.23 billion from $5.25 billion;

Spending on technology and content increased 28.3% to $16.09 billion from $12.54 billion.

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