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Asking rents declined at downtown Boston office properties as the availability rate approached 20 percent at the end of 2022, the highest level in two decades.

The downtown market had 369,115 square feet of negative absorption in the fourth quarter, CBRE reported, as the direct vacancy rate rose to 12.5 percent and availability rate hit 19.9 percent.

As office leasing declines amid lease expirations and the lingering hybrid workspace model, the downtown Boston market had nearly 1.4 million square feet of negative absorption in 2022.

Sublease offerings continue to add inventory to the market, with 515,000 square feet of new listings during the fourth quarter. Tech companies account for a big portion of the listings, comprising 43 percent of all sublease listings. There are 19 blocks of sublease space above 50,000 square feet, CBRE reported.

Overall deal activity increased 10 percent from 2021 to 4.8 million square feet.

But asking rents have fallen for three consecutive quarters, ending the year at $66.60 per square foot on a gross basis.

On a submarket basis, the central business district accounted for the largest volume of leasing at 362,000 square feet in the fourth quarter, including a 36 percent share of renewals.

Availability rates range from 25.2 percent in the central business district to 7.9 percent in Fenway/Kenmore Square, the only submarket with single-digit availability rates. The 15.5 million-square-foot Back Bay market remained relatively resilient, with a 13.1 percent availability rate. But reflecting the quiet leasing climate, the largest deal of the quarter was a 34,500-square-foot renewal and expansion by Weiss Asset Management at 222 Berkeley St.