Nearly one in six Portland homes listed on Airbnb operate essentially as full-time vacation rentals, an analysis by the data journalism website FiveThirtyEight found, a higher ratio than any U.S. city examined except Honolulu.

The analysis found that Airbnb, a website that lets users easily rent their property to travelers like a hotel, has likely had little effect on housing prices to date. But it also said the full-time "commercial" rentals are the most likely to push housing costs higher because they might otherwise be rented out to locals.

What's more, Airbnb depends on these commercial-tier rentals for 40 percent of its revenue in Portland, the analysis found, so the company's business depends on growing their ranks.

FiveThirtyEight defined "commercial" Airbnbs as those rented out 180 days a year or more. That's enough time to account for every weekend day plus five work weeks.

Airbnb disputed the analysis. A company spokesman was quoted as saying 180 days was an arbitrary threshold, and said many of the qualifying listings might actually be commercial enterprises like boutique hotels or guest houses that use the platform.

The company has also argued that it helps residents combat rising housing costs by providing an extra stream of income.

The analysis found Portland has 2,700 active Airbnb listings in all, which represents just 1 percent of its overall housing stock. Given the relatively small number of units, the impact on housing prices currently is likely small, FiveThirtyEight said, quoting several housing and land-use experts.

Portland sought to rein in the impact on housing prices by requiring that owners live in the home they're renting out at least nine months out of the year, though an analysis by Willamette Week last year found numerous examples of apparent violations.

Airbnb has another tie to Portland: its North American operational headquarters, which opened in 2014 in Old Town Chinatown and has more than 200 employees.

-- Elliot Njus

enjus@oregonian.com

503-294-5034

@enjus